Denon AVR-X3700H AVR Review

[amper42]

Is there any measurement of how the receiver affects noise on the preamp outputs on a separately assigned "zone 2" channel?

In Pre-amp mode Denon Zone 2 is non-functional. If you use an amp assign mode that supports Zone 2, then the amp measurement will be the same as any internal amp on the Denon 3700.

On another note, I tried using Zone 2 to power a secondary pair of speakers in the same room. I discovered that's not possible as there is a slight delay in the output with Zone 2. I was unable to determine why that might occur.

 

[kevin1969]

In Pre-amp mode If you use an amp assign mode that supports Zone 2, then the amp measurement will be the same as any internal amp on the Denon.

Did you mean to say that the zone2 preamp measurement will be the same as the amp measurement?

There is a slight delay in the output with Zone 2. I was unable to determine why that might occur.

You mean when you're powering both zones with the same source there's actually a delay on the zone 2 speakers???

 

[amper42]

Did you mean to say that the zone2 preamp measurement will be the same as the amp measurement?



You mean when you're powering both zones with the same source there's actually a delay on the zone 2 speakers???

Yes, if you try to play Zone 2 in the same room as the main speakers on the Denon 3700 there is a slight echo delay in the sound. It's pretty strange.

 

[kevin1969]

Yes, if you try to play Zone 2 in the same room as the main speakers on the Denon 3700 there is a slight echo delay in the sound. It's pretty strange.

Are you using a digital music source? If so I'm wondering if the same delay occurs when it's playing both zones from an analog source.

My primary and secondary zones are basically in adjacent rooms and that would drive me crazy.

 

[amper42]

Are you using a digital music source? If so I'm wondering if the same delay occurs when it's playing both zones from an analog source.

I was trying to use Zone 2 with the Denon in the same room. That lasted about 1 hour as the Zone 2 speakers had a slight delay (echo) which made it impossible to use in the same room. This occurred with analog CD source or using DLNA with Qobuz. It appears the design for zone 2 outputs are intentionally designed to be used in a different room. (Otherwise, the slight delay would drive me crazy.)

 

[kevin1969]

Yes, if you try to play Zone 2 in the same room as the main speakers on the Denon 3700 there is a slight echo delay in the sound. It's pretty strange.

In the manual for the 3700H it says you have to enable All Zone Stereo for the output to sync up.

Have you tried this ?

 

[AllCourtGuy]

My Denon 4700 is running in preamp mode. All of my speakers are powered by ext. amps. The Denon still gets pretty warm. I would have thought in preamp mode it would run cool but that's not the case. However, with the AC Infinity MULTIFAN S7 fan on top it stays amazingly cool.

I am curious, do you have the fans standing up on the back of the abr and blowing across the top, or laying down on the top and pulling air directly from the avr?

 

[amper42]

I lay the fans on top of the Denon Receiver blowing air up toward the ceiling. It's amazingly effective for keeping the unit cool.

 

[danillll]

Hi,
I need help deciding between the x3700h and the Anthem SR7013.
I understand the difference between the 2 when it comes to supported audio formats and video processing and that the Denon has way more features.

I am mainly interested in the onboard amp and the quality of processing;
would the Denon be able to drive 4 ohms LCR speakers THX-365IW ? I am aware that the ideal solution is to have an external amp, but due to limited budget, I was hoping I can use the AV receiver amp for ~ year before I adding an external amp. Or you think the Anthem has more juice to power 4 ohms speakers.
What about the processing quality, I read that the Denon is more neutral than the Anthem, is this a true statement?

Thanks in advance for all your help

 

[peng]

Hi,
I need help deciding between the x3700h and the Anthem SR7013.
I understand the difference between the 2 when it comes to supported audio formats and video processing and that the Denon has way more features.

I am mainly interested in the onboard amp and the quality of processing;
would the Denon be able to drive 4 ohms LCR speakers THX-365IW ? I am aware that the ideal solution is to have an external amp, but due to limited budget, I was hoping I can use the AV receiver amp for ~ year before I adding an external amp. Or you think the Anthem has more juice to power 4 ohms speakers.
What about the processing quality, I read that the Denon is more neutral than the Anthem, is this a true statement?

Thanks in advance for all your help

The SR7013 has slightly stronger amps but not enough to make a real difference practically speaking. You can save some money if you can find an AVR-X4500H that has the same amp section as the 7013.

Whether they can drive your THX-365IW or not depends on your actual power requirement, that in turn depends on your seating distance, and how loud you listen to music and movies. You can use an online calculator to figure your need. Without knowing your actual power requirement, I would say if you want to push those speakers to their limits, the AVR-X3700H or even the SR7013, or AVR-X4500H are not going to do it. The MRX720, 740 is not more powerful than the Denon/Marantz, their output specs are all in the same ball park.

As for processing quality, that's hard to say because it depends on you preference. Without processing, that is, direct/pure direct mode, Anthem claimed to design for neutrality too.

In their FAQ, Anthem stated:
Frequently Asked Questions | Anthem® (anthemav.com)

"Do the amps have a warm sound or a bright sound?
None of our components are designed with a "sonic flavor" other than playing exactly what's in a recording. Unfortunately with pop CD mastering, pushing levels way into overload regardless of how much distortion this adds is all too common. Recordings of acoustic instruments with minimal or no processing during mastering sound more natural, therefore they are a much better test of how natural-sounding the playback equipment is.
Are they better suited for music or for movies?
Sound reproduction equipment doesn't know the difference between a music signal and a movie signal, or for that matter the musical score within a movie soundtrack. Accurate for one means accurate for the other."

Unfortunately, there are too much hearsay on the internet, that led people to continue to believe in audio myths.

 

[danillll]

The SR7013 has slightly stronger amps but not enough to make a real difference practically speaking. You can save some money if you can find an AVR-X4500H that has the same amp section as the 7013.

Whether they can drive your THX-365IW or not depends on your actual power requirement, that in turn depends on your seating distance, and how loud you listen to music and movies. You can use an online calculator to figure your need. Without knowing your actual power requirement, I would say if you want to push those speakers to their limits, the AVR-X3700H or even the SR7013, or AVR-X4500H are not going to do it. The MRX720, 740 is not more powerful than the Denon/Marantz, their output specs are all in the same ball park.

As for processing quality, that's hard to say because it depends on you preference. Without processing, that is, direct/pure direct mode, Anthem claimed to design for neutrality too.

In their FAQ, Anthem stated:
Frequently Asked Questions | Anthem® (anthemav.com)

"Do the amps have a warm sound or a bright sound?
None of our components are designed with a "sonic flavor" other than playing exactly what's in a recording. Unfortunately with pop CD mastering, pushing levels way into overload regardless of how much distortion this adds is all too common. Recordings of acoustic instruments with minimal or no processing during mastering sound more natural, therefore they are a much better test of how natural-sounding the playback equipment is.
Are they better suited for music or for movies?
Sound reproduction equipment doesn't know the difference between a music signal and a movie signal, or for that matter the musical score within a movie soundtrack. Accurate for one means accurate for the other."

Unfortunately, there are too much hearsay on the internet, that led people to continue to believe in audio myths.

@peng
Great info! Thanks!
I was considering the 3700 because of the great reviews. My dilemma is if I go with 4500 and sacrifice the other features that 3700 brings and find out that it's still lacking power or the extra power, like you've said, is not enough; so I might still end up with an amplifier.

You've mentioned that i can measure how much power I need, do you mind pointing me to those tools? MLP is 14-15 feet from the center speaker.
I have not bought those speakers yet, if you have other recommendations for in wall LCR that are on par with the Monolith and runs on higher impedance to avoid extra amp?

Finally, quick question regarding the amp, can I buy a 3-4 channels amp to only run the LCR and keep the av receiver to power the remaining speakers , or is it pre amp all or nothing? Also any suggestion for a budget friend amp.

Thanks for answering all my newbie questions

edit: oh, one last question, when the specs show, for example, 120 watt per channel, does it mean it can deliver 120 watt per channel for each channel (assuming they all simultaneously emitting sound) or 120 watt per channel when others are not working and this number goes down when 2 or more channels are simultaneously working
I think I found the calculator you've mentioned

 

[amper42]

@peng
Great info! Thanks!
I was considering the 3700 because of the great reviews. My dilemma is if I go with 4500 and sacrifice the other features that 3700 brings and find out that it's still lacking power or the extra power, like you've said, is not enough; so I might still end up with an amplifier.

You've mentioned that i can measure how much power I need, do you mind pointing me to those tools? MLP is 14-15 feet from the center speaker.
I have not bought those speakers yet, if you have other recommendations for in wall LCR that are on par with the Monolith and runs on higher impedance to avoid extra amp?

Finally, quick question regarding the amp, can I buy a 3-4 channels amp to only run the LCR and keep the av receiver to power the remaining speakers , or is it pre amp all or nothing? Also any suggestion for a budget friend amp.

Thanks for answering all my newbie questions

edit: oh, one last question, when the specs show, for example, 120 watt per channel, does it mean it can deliver 120 watt per channel for each channel (assuming they all simultaneously emitting sound) or 120 watt per channel when others are not working and this number goes down when 2 or more channels are simultaneously working
I think I found the calculator you've mentioned

1. I would not take a Denon 4500 over a Denon 3700. The 4500 is old tech. The 3700 offers pre-amp mode which isn't available on the 4500. That's a big difference for me. The extra power of the amps in the 4500 won't even be noticible.

2. You can use this calc to determine SPL your speakers will reach with the 3700. My guess is it will be fine unless you listen at unhealthy volume levels. http://myhometheater.homestead.com/splcalculator.html

3. The Monolith by Monoprice THX-365IW offer 89dB sensitivity. They will easily be powered by the Denon 3700.

4. The amp power specs on the Denon receivers are typically good for 2 channels running. If you are running all 9 channels you should expect the 105W per channel to be closer to 85W, especially in Multi-channel Stereo mode. You should also realize most of us are listening at levels of just a few watts for 70dB. The Monolith speakers will produce 100dB even with only 70W.

5. Stay with the Denon 3700. If you absolutely want Auro-3D get the Denon 4700 instead. After owning the 4500, I wouldn't even consider it anymore. I would definitely recommend buying a Denon 3700 over a Denon 4500.

 

[danillll]

1. I would not take a Denon 4500 over a Denon 3700. The 4500 is old tech. The 3700 offers pre-amp mode which isn't available on the 4500. That's a big difference for me. The extra power of the amps in the 4500 won't even be noticible.

2. You can use this calc to determine SPL your speakers will reach with the 3700. My guess is it will be fine unless you listen at unhealthy volume levels. http://myhometheater.homestead.com/splcalculator.html

3. The Monolith by Monoprice THX-365IW offer 89dB sensitivity. They will easily be powered by the Denon 3700.

4. The amp power specs on the Denon receivers are typically good for 2 channels running. If you are running all 9 channels you should expect the 105W per channel to be closer to 85W, especially in Multi-channel Stereo mode. You should also realize most of us are listening at levels of just a few watts for 70dB. The Monolith speakers will produce 100dB even with only 70W.

5. Stay with the Denon 3700. If you absolutely want Auro-3D get the Denon 4700 instead. After owning the 4500, I wouldn't even consider it anymore. I would definitely recommend buying a Denon 3700 over a Denon 4500.

View attachment 113650

@amper42 Thank you!!!!
I am convinced! about to click on the 3700 buy button one last thing to clarify, the calculator, the sensitivity spec, is this for 1w/1m or 2w/1m as it's a 4ohms impedance, this is the only piece that confused me. According to the spec it's "Sensitivity = 89.5dB (2.83V@1m)" so if I want to concert V to W, it will be P=V2/R=2.83*2.82/4=2W@1m and all the calculators uses 1W/1m

Thanks

 

[amper42]

@amper42 Thank you!!!!
I am convinced! about to click on the 3700 buy button one last thing to clarify, the calculator, the sensitivity spec, is this for 1w/1m or 2w/1m as it's a 4ohms impedance, this is the only piece that confused me. According to the spec it's "Sensitivity = 89.5dB (2.83V@1m)" so if I want to concert V to W, it will be P=V2/R=2.83*2.82/4=2W@1m and all the calculators uses 1W/1m

Thanks

Absolutely, don't worry about it. The Denon 3700 will play these speakers louder than you can stand. lol

The beauty of the 3700 is it's pre-amp mode allows you to use external amps to power every speaker and completely bypass the internal amps. However, for the speakers you have selected the Denon 3700 will be fine. If you need it louder I would suggest also budgeting for an ear doctor.

 

[danillll]

Absolutely, don't worry about it. The Denon 3700 will play these speakers louder than you can stand. lol

The beauty of the 3700 is it's pre-amp mode allows you to use external amps to power every speaker and completely bypass the internal amps. However, for the speakers you have selected the Denon 3700 will be fine. If you need it louder I would suggest also budgeting for an ear doctor.

Thank you!

 

[peng]

@amper42 Thank you!!!!
one last thing to clarify, the calculator, the sensitivity spec, is this for 1w/1m or 2w/1m as it's a 4ohms impedance, this is the only piece that confused me. According to the spec it's "Sensitivity = 89.5dB (2.83V@1m)" so if I want to concert V to W, it will be P=V2/R=2.83*2.82/4=2W@1m and all the calculators uses 1W/1m

Thanks

That is correct, when you use that calculator based on 4 Ohm speakers, you should subtract 3 dB from the sensitivity spec. Instead of entering 89.5 dB you should enter 86.5 dB. Or you can just enter 89.5 dB, but whatever the calculated result is, subtract 3 dB. Simply put, either do the compensation upfront or do it after.

 

[peng]

@peng
Great info! Thanks!
I was considering the 3700 because of the great reviews. My dilemma is if I go with 4500 and sacrifice the other features that 3700 brings and find out that it's still lacking power or the extra power, like you've said, is not enough; so I might still end up with an amplifier.

As I said before, the differences in output between the X3700H and SR7013 are not enough to make a noticeable difference. And I only mentioned the X4500H because you mentioned the SR7013, that will cost you more and you get less, unless you need multichannel analog inputs and/or you like the way it looks.

The X3700H is the better choice imo, but if you want the front HDMI port and Auro 3D, then if the prices are the same, the X4500H may be worth considering as long as you can still get one brand new with full manufacturer's warranty. Other than that, again, the X3700H is the best bang for the dollar at the moment.

You've mentioned that i can measure how much power I need, do you mind pointing me to those tools? MLP is 14-15 feet from the center speaker.
I have not bought those speakers yet, if you have other recommendations for in wall LCR that are on par with the Monolith and runs on higher impedance to avoid extra amp?

You can use the calculator amper42 linked, but since you provided the required info, I did it with my own calculator and the results are:

Based on the results, if your target SPL from 14.5 ft/4.42 m (average of your 14-15 ft) is not more than 95-98 dB peak, you should be able to use the AVR-X3700H safely, but a fan on top would be needed to keep it cool for longevity.

If your target is, say, 100 to 103 dB, that's still a few dB below THX reference level of 105 dB peak, then an amp rated 300 W into 4 Ohm would be a good idea. And all that are based on factoring in 3 dB of room gain (that affects mostly the bass range) already.

Setting XO to 90 Hz, or 80 Hz but not lower should help too. The thing about using mid range AVRs to drive such real 4 Ohm speakers with sensitivity in the high 80 and above range is that you can do it for sure, depending on the distance from the speakers and your desired SPL and you have to be a little more disciplined with the volume setting. The same should apply to separate power amps as well, but all else being equal, they typically have large power supplies, beefier heat sinks and output devices so even if rated the same as an AVR, they can do the same job in a more relax way.

Finally, quick question regarding the amp, can I buy a 3-4 channels amp to only run the LCR and keep the av receiver to power the remaining speakers , or is it pre amp all or nothing? Also any suggestion for a budget friend amp.

You can do that but then you cannot use the preamp mode. Preamp mode is all or none, when used, all internal amps will be disconnected from the pre outs.

edit: oh, one last question, when the specs show, for example, 120 watt per channel, does it mean it can deliver 120 watt per channel for each channel (assuming they all simultaneously emitting sound) or 120 watt per channel when others are not working and this number goes down when 2 or more channels are simultaneously working
I think I found the calculator you've mentioned

amper42 answered your question already, I tend to be more conservative on this so I would say go with the measurements Amir provided. If you go by D+M's, you can expect about 70% of the rated output when 5 channels are driven simultaneously.

For 7 channel driven simultaneously, my guess is, about 60%-70% based on various bench test results I have seen, but that would be based on 1% THD+N, at 1 kHz. Likewise, for 5 channel driven, my guess based on past measurements, it would like be about 75-78%. Again, better go with Amir's measurements, just be aware that his numbers in % would be lower because the denominator he used were based on the measured two channel outputs and that typically would be lower than D+M's specified two channel outputs. Keep in mind the 5,7 channel driven simultaneously ratings are for short duration only, and for real world use such as watching movies, I don't believe it is as much a concern as people think it is because in most movies, it is not likely that 7 channels would be driven to the same maximum level "simultaneously". In such rare occasions, it wouldn't last longer than a few seconds either.

 

[danillll]

@peng

As I said before, the differences in output between the X3700H and SR7013 are not enough to make a noticeable difference. And I only mentioned the X4500H because you mentioned the SR7013, that will cost you more and you get less, unless you need multichannel analog inputs and/or you like the way it looks.

The X3700H is the better choice imo, but if you want the front HDMI port and Auro 3D, then if the prices are the same, the X4500H may be worth considering as long as you can still get one brand new with full manufacturer's warranty. Other than that, again, the X3700H is the best bang for the dollar at the moment.

Right, I was under the impression that the extra power is significant, but as you have corrected me and from what I've learned in the past 24 hours, it's not enough to go with an older tech.

You can use the calculator amper42 linked, but since you provided the required info, I did it with my own calculator and the results are:

dude! thank you man! you rock for going the extra mile and help a stranger. Thank you!

I found this excel sheet http://www.acousticfrontiers.com/2013322spl-calculator/ and it gave me different results.
This is with headroom of 10 to bring up the total decibel to 95, similar to what you used, but as you can see the watts needed is much lower.
Maybe the math is wrong here? The only difference is that I have set the baffle wall to "yes" which is accurate in my case, as those are in-wall speakers.

But if I try to hit the THX peek of 105db by setting the headroom to 20db then the needed power will jump drastically to higher value that the speaker peak limit of 200w . Does this mean that those speakers can't reach THX level in my room/distance?

What is the safe power limit per channel for 4ohms impedance, I know this is not published by the vendor, but reading the review made by the OP, can I assume the value of ~160W on 4ohm is a number we go with?

If your target is, say, 100 to 103 dB, that's still a few dB below THX reference level of 105 dB peak, then an amp rated 300 W into 4 Ohm would be a good idea. And all that are based on factoring in 3 dB of room gain (that affects mostly the bass range) already

not that I want to, but it looks like one will never reach the thx reference of 105db regardless of the amp in use, unless sitting very close to the speakers . As if I read the spec on the speakers, the max peak is 200W

Setting XO to 90 Hz, or 80 Hz but not lower should help too. The thing about using mid range AVRs to drive such real 4 Ohm speakers with sensitivity in the high 80 and above range is that you can do it for sure, depending on the distance from the speakers and your desired SPL and you have to be a little more disciplined with the volume setting. The same should apply to separate power amps as well, but all else being equal, they typically have large power supplies, beefier heat sinks and output devices so even if rated the same as an AVR, they can do the same job in a more relax way.

Good point, I have a good SVS sub, so that should help.

You can do that but then you cannot use the preamp mode. Preamp mode is all or none, when used, all internal amps will be disconnected from the pre outs.

I stayed up till 3:00 am reading and learning last night. So one thing I found is that you can do L,R pre-amp by setting the config to 11.1 and turn off the non-existing speakers https://www.audiosciencereview.com/...-avr-review-updated.14493/page-66#post-557465
I assume this is a valid option, so I can do L, R pre-amp and the Center Pre-out . My understanding is that pre-amp means you are getting the raw signal after being processed and pre-out means I am getting the signal amplified by the receiver and it will be also amplified by the external amp. Is this accurate description of the difference between pre-amp and pre-out?

I am pulling the trigger on this receiver this afternoon, from what you and @amper42 explained and what I have read, this will be my best option and in the future, if I need to drive the speakers higher, then I can add external amp for the L,R pre-amp and C pre-out ; my remaining speakers will be 8ohm.

 

[peng]

@peng



Right, I was under the impression that the extra power is significant, but as you have corrected me and from what I've learned in the past 24 hours, it's not enough to go with an older tech.




dude! thank you man! you rock for going the extra mile and help a stranger. Thank you!

I found this excel sheet http://www.acousticfrontiers.com/2013322spl-calculator/ and it gave me different results.
This is with headroom of 10 to bring up the total decibel to 95, similar to what you used, but as you can see the watts needed is much lower.
Maybe the math is wrong here? The only difference is that I have set the baffle wall to "yes" which is accurate in my case, as those are in-wall speakers.
View attachment 113749


But if I try to hit the THX peek of 105db by setting the headroom to 20db then the needed power will jump drastically to higher value that the speaker peak limit of 200w . Does this mean that those speakers can't reach THX level in my room/distance?

View attachment 113750

What is the safe power limit per channel for 4ohms impedance, I know this is not published by the vendor, but reading the review made by the OP, can I assume the value of ~160W on 4ohm is a number we go with?




not that I want to, but it looks like one will never reach the thx reference of 105db regardless of the amp in use, unless sitting very close to the speakers . As if I read the spec on the speakers, the max peak is 200W



Good point, I have a good SVS sub, so that should help.



I stayed up till 3:00 am reading and learning last night. So one thing I found is that you can do L,R pre-amp by setting the config to 11.1 and turn off the non-existing speakers https://www.audiosciencereview.com/...-avr-review-updated.14493/page-66#post-557465
I assume this is a valid option, so I can do L, R pre-amp and the Center Pre-out . My understanding is that pre-amp means you are getting the raw signal after being processed and pre-out means I am getting the signal amplified by the receiver and it will be also amplified by the external amp. Is this accurate description of the difference between pre-amp and pre-out?

I am pulling the trigger on this receiver this afternoon, from what you and @amper42 explained and what I have read, this will be my best option and in the future, if I need to drive the speakers higher, then I can add external amp for the L,R pre-amp and C pre-out ; my remaining speakers will be 8ohm.

Just two quick points for you:

The Acoustic Frontier calculator is much better than the Homestead one but it requires the user to be more knowledgeable otherwise it would give you weird results as you are getting.

For example, you entered "Yes" to baffle wall, but I assume you don't have a baffle wall. Also, you entered 85 dB for your targeted program SPL, I used 75 dB, or 95 dB with the build in THX 20 dB "headroom" because I know you won't be able to achieve 105 dB anyway so I just wanted to try and see if 95 dB is achievable.

So if you change the baffle wall to "No", and the 85 dB average program to 75 dB, the calculator will 141 W peak, 71 W average, that's almost the same as my calculated 69.58 W average, 139.16 W peak.

That minute difference is due to our assumption of room gain. I assume 3 dB room gain, and he assume it to follow a formula based on distance. The difference is so little, that I decided not to bother further complicated the calculator.

We both used Excel to do the calculation. There is no right or wrong as there are assumptions made that could only approximate reality, but obviously I like my better otherwise I would just use his.

 

[peng]

@peng

What is the safe power limit per channel for 4ohms impedance, I know this is not published by the vendor, but reading the review made by the OP, can I assume the value of ~160W on 4ohm is a number we go with?

You wish! Put it this way, the X3700H is rated 105 W into 8 Ohms. So in theory, it is safe to rate it 105/2 = 52.5 W into 4 Ohms based on current. As a given voltage output, the current flow to a 4 ohm load will double that flows into an 8 Ohm load.

In practice, it will actually deliver more "power" into a 4 Ohm resistor load as shown in Amir's measurements, but that would be based on shorter duration. It is for that reason that Denon, Marantz, Yamaha and others all want you to set to impedance to 4 Ohm when using 4 Ohm speakers, because if they don't they would not likely get the regulatory approval they need to sell in various markets.

Reviewers, however, may suggest that it is okay, in fact you should leave it in the 8 Ohm setting. That's because they know a responsible user will not abuse their unit by using real 4 ohm nominal speakers and blast highly compressed music all day long at loud level.

not that I want to, but it looks like one will never reach the thx reference of 105db regardless of the amp in use, unless sitting very close to the speakers . As if I read the spec on the speakers, the max peak is 200W

That's right, but you can get close, to may be 102-103 dB peak, if you pair it with something like the Monolith 200 W amp that can output a little more than 300 W into 4 Ohms.

I stayed up till 3:00 am reading and learning last night. So one thing I found is that you can do L,R pre-amp by setting the config to 11.1 and turn off the non-existing speakers https://www.audiosciencereview.com/...-avr-review-updated.14493/page-66#post-557465
I assume this is a valid option, so I can do L, R pre-amp and the Center Pre-out . My understanding is that pre-amp means you are getting the raw signal after being processed and pre-out means I am getting the signal amplified by the receiver and it will be also amplified by the external amp. Is this accurate description of the difference between pre-amp and pre-out?

Yes that is an option, in fact I linked that post many times before.

and in the future, if I need to drive the speakers higher, then I can add external amp for the L,R pre-amp and C pre-out ; my remaining speakers will be 8ohm.

As you know, you won't be able disconnect the center channel amp but in your case it won't matter as it would be extremely unlikely that the pre outs will go higher than 1.5 V anyway, unless you pick a power amp that has really low gain. In fact, the same applies to the L,R speakers as well, but if you can disconnect the internal amps, then you just do it, nothing to lose.