So we can’t just look at some DAC or some SINAD numbers and say that one AVP should sound the same as another?
The answer to that question NO. The reason is because those measurements ignore the fourth dimension of the universe, which is TIME.
SINAD tells you nothing about time, which is another way of saying phase coherent equipment and comparing one piece of equipment to another.
I have long been concerned about the time relationships of audio equipment. The tendency is to say because this is difficult and gear, especially speakers, are awash in time misalignments, that it does not matter. Oh, but it does!
The SNR improvement of the AV 10 over the 7706 is huge and would by itself result in audible improvement.
However, I have taken a lot of trouble to minimize phase shifts/time shifts in my speaker designs. It is almost impossible to avoid in speakers and have a decent FR. My front three do have some time shift at 2,500 Hz, but the other points of crossover are time coherent.
The surrounds have a very minimal time shift at 3000 Hz, the rear speakers only have a time shift at 180 Hz, where I doubt it is significant, through the rest of the range they are time coherent. The ceiling Atmos speakers have no time shift.
So, yes this unit does sound better on two channel, but the improvement becomes more noticeable as you add channels.
So my strong hunch is that the improvement I am hearing is down to time. That will not show up in SINAD.
Again, I did not buy my AV 10 with the expectation that would be a highly noticeable improvement in SQ. I bought it because I am trouble averse, and the 7707 and 7706 had worn out their welcome for reliability. I have to say though, that the superb SNR of the AV 10 was a consideration. As you add channels a good SNR becomes of increasing importance. The fact the room is totally, and I mean totally silent with no signal, I believe is a significant contributor to the improved SQ.