Would/can someone explain in plain language how the preamp/preout mode works vs using the internal amps? I've read from several other sources the actual words that the user can "turn off" the internal amps for use with external amps. What I'm understanding from the test in this form is that the if some and not all of the internal amps are used, the unused amps cause distortion AND if the AVRs are used in pre -out mode, the unused internal amps cause distortion in the signal being sent to an external amp. it's all about as clear as mudd for someone like me who is trying to understand whether I'll be getting less distortion using only 5 internal amps in my 5.2 speaker setup or if I will in fact just be sending additional distortion to an external amp if I use the preamp mode? It gets even muddier when considering 4 ohm speakers...if the amp distortion nearly doubles when connected to 4 ohm speakers, wouldn't it make sense to send the cleaner signal to an external amp that has much less distortion into a 4 ohm speaker? Is this a question I should be asking Amirm? If so, how do I get a question directly to him? Thanks.
I imagine you are referring to the Denon 4700 from this forum.
In principle for a 5.1 system it will not need external amplification, and according to Amir's measurements it will have a high Sinad, very little distortion, above Denon's reference volume (up to 1.4v, which corresponds to an approximate volume of 82 or +2 depending on the scale).
If you still want to add an external amplifier, in this model you can turn off the amplification for all channels, "all or nothing", it is the new "preamplifier" mode of the 2020 Denon and Marantz configuration.
This way , and with the appropriate external amplifiers, you can have a cleaner sound beyond 1.4v, but in normal use below the reference volume there will be no difference, and at a higher volume it will be difficult to distinguish.
Finally, you have the possibility of "disconnecting" exclusively the internal amplification of the front channels (L / R), if in the initial configuration you indicate that you have 11 speakers (even if you do not use all the channels), and connect to the preout outputs L / R of the avr the external amplifier. This won't add any noticeable noise or distortion either.
The question is when using external amplifiers without using the full pre-amplification mode, or if, for example, in addition to disconnecting and externally amplifying the front ones, you intend to amplify other channels, for example the center speaker, because the internal amplifier of the rest of the channels they cannot be disconnected (only the Denon x8500h can turn them off individually).
In any case, I think you shouldn't worry too much about all this, it is very difficult to see differences by adding external amplifiers after calibration, and from what we have already commented.
And if this really worries you, you can use either of the two methods discussed above, the full preamp mode, or the disconnection and external amplification only of the front ones.
With the 4 Oh speakers you will have no problem in a 5.1 setup, even if you use the avr's internal amplification. Only in the case of adding more channels, or in large rooms, you will need external amplification and you will have to take into account what we have commented before.