Ok, so the situation is the following.
The setup with the 7015 used to be, while using it in FULL PREAMP MODE:
7.0 (FL, C, FR, SL, SR, SBL, SBR) through the pre amp section, using external amplifier (Sherbourn PA 7-150)
4 Atmos (TML, TMR, TRR, TRL) through the pre amp section, using external amplivier (Emotiva BasX A4)
I have read earlier the review of Amir of the SR7015, and saw that even with the Full Pre Amp mode engaged, the optimal max Pre Out output is around 0.7 volts. I have checked the Sherbourn's gain and counted that I would max. at 100W per channel if I give it a 0.7 v signal (the amp is capable of delivering 150W 8 ohm per channel at 1.2 V signal).
0.7 V, 100 W is about right, but at 1.2 V, it will output about 285 W, the 150 W you cited is probably for all 7 channels driven simultaneously and even then it is the rated output specified by Sherboun, the calculated value should be about 285 W, with 1.2 V input. It probably could do even >300 W on short term, or transients at a little higher distortions.
Now that I had to remove the Sherbourn temporarily out from the equation (as it had to be taken to the service), I have connected the 7.0 channels into the Marantz directly and left the 4 Atmos speakers being amplified by the Emotiva, and set the Marantz to 11.1, instead of Full Pre Amp mode.
As it almost sounds identical now (with Marantz "mixed mode", using partially the internal amp),
If you do a blind test, I bet 5 to 1, you will not be able to guess right more than say, 12 out of 20 times no matter how hard to try.
I have been thinking if I should go for the 8015 for more power and just keep the Emotiva for the 4 Atmos speakers. I have read in the other review of Amir of the SR8015, that it has a stable 2.0 v output through the pre amps with Full Preamp Mode engaded.
I thought I've already explained that those AVRs can output a lot more than 2 V (read the related specs and measurements, such as the vol IC, opa datasheets instead of internet hearsay), how high it could go depends on how much distortions you can live with, the maximum value, that is, before clipping (say, define that as either 0.1 or 1% THD as most reviewers do) of about 4 V, say 3.7 to 4.5 V depending on the test conditions. You are going to read a lot of stuff on the internet, so I understand why your have such questions, or doubts, you came to the right place though,
here you will get more opinions, and some often include backup information to support their claims/opinions.
Therefore, if I put the Sherbourn back into the system it will properly be fed by the SR8015. BUT I have been thinking of getting rid of the Sherbourn totally and just using the 8015 in mixed mode (exactly the same way how the 7015 is now being used) and so I can get more power from the 8015's Toroidal power supply for the 7.0.
Couple of points: 1) You have the Sherborn already, why not keep it? In case your power need changes in the future such as upgrading speakers, increasing your seating distance, and/or you want to listen much louder than you do now then the Sherbourn's additonal reserve will be there for you. 2) Forget about the toroidal thing, at the level of your very nice AVRs such as the 7015, even 6015, EI or toroidal is not important, each design has their pros and cons. The output power is a function of the VA rating of the transformer, not its geometric shape of E-I, toroid, or something else. Don't fall for those hypes. You will get more power reserve from the 8015, but not because its transformer is toroidal. In practical term, the difference in max outputs between the 7015 and 8015 is very marginal, you
will not be able to hear a difference as in dB term, it will be less than 1 (about 0.8) dB, think in terms of a couple of clicks (not even) on the volume button will more than account for the difference in decibel level you hear.
If however I can't use the 8015 in mixed mode, and so I have to keep the Sherbourn anyway for the 7.0, then although I can feed it with a stronger signal with full preamp mode from the 8015, I think I would better be buying a Cinema 40, that in theory has a better pre amp stage aswell than the 7015, and it is also cheaper than the 8015.
I think you are right, while the 8015 has much better build quality, but if your goal is functionality and/or sound quality related, the C40 is better. All those copper plates, additional shielding, toroidal transformer, better HDAM version etc., don't mean anything in terms of sound quality; and perhaps some legacy connections, that are of course totally useless if you don't use them.
The C40's additional subout features, DL options, and the more up to date DSP chips are things that matter to sound quality for sure, depending on your particular applications. The 8015 does have an advantage in terms of the DAC IC, but that's only if you can get one that is manufactured before the shortage after the AKM factory fire, the newer oness will all have the same DAC IC that the C40 has. In fact, if your 7015 is the earlier version that has the original AKM dac, such as the one Amir tested, then it should perform better on paper than the 8015 and the C40, but on paper only as I highly doubt humans can hear the difference just because one has a few dB higher SINAD.
Now back to the misconception you seem to have with Amir's graphs and comments, if you are ocd (like me and many others) about pre out SINAD vs output, then you should focus on the graphs that Amir typically inclued (can't thank you enough for going the extra mile, unlike some other reviewers), and forget what you need about those references/comments based on a single point, such as THD+N at 1 V, 2 V etc.
So, let's take a look:
In non-preamp mode, the 7015's SINAD is about 90 dB at below 0.3 V, and about 75 dB at just over 2 V, it will likely be around 65 to 70 dB even at 4 V if you extend the curve, or refer to the Denon AVR-X6700H, that Amir measured it to over 4 V.
The 0.7 V, as Amir commented, is only "optimal" because it is the peak within the range of 0 to the clipping point. Amir did refer to "clipping" at the 1.4 to 1.5 V but that's because he called it "clip", when he saw SINAD started to drop much quicker at that point. I disagree with him, but he's boss. I know I am right, or at least in the practical sense, and I have explained my rational a couple time, obviously those posts have since been buried among the thousands of ASR posts, whereas Amir's comments will stick forever, and many would undoubtedly be misled unless they dig deep...
Amir only measured those AVRs pass 4 V once (or twice, maybe), so those who wonder how high can the D+M unit's pre out will go before clipping, should value the one he did on the Denon X6700H:
All those AVRs have the same DAC and volume IC, and in some case OPA buffer, inlcuding Marantz's HDAMs, so you can expect very similar pre out limit: