When you are in a store in their listening room and auditioning several AVRs, they all sound a little different. You choose one, bring it home and it doesn't sound even close to what you heard in the store. Why? Because your room is different. I already know, I don't like the 2 channel sound of Denon X4700H with my Focal 926. It is too late for me to return the Denon, and too late to return speakers I invested $5K into. I have to make it to work somehow. I know the Denon X4700H has an excellent preamp and a streamer for any devices using HDMI port. I auditioned Arcam SA30 as a power amp and got the sound I like with ease. If an Arcam PA240 meets or exceeds the sound quality I like, I will keep it. I have not explored the Arcam's Dirac live, may be once I get to it, it will be the game changer.
It has been said, and explained by experts in the field (including our respected Dr. Toole, Dr. Olive etc.) that if you perceived "sound quality" in sighted tests in which you know which device you listened to, then it doesn't matter what you think. The thing is, unless you take the time to do comparisons that follows generally accepted protocols such as to make sure you won't know which device you listen to, no one here can change your mind. If you do take the time like some of us have, then you will learn the truth. It is of course up to you to weigh the benefits of knowing the truth, or ignoring it for better reasons (I can think of at least one such benefit of ignoring blind tests). Some of us on this forum can say, been there, done that on this well design amps sound the same, or not thing lol..
In my case, just learning/knowing the truth, has saved me hard earned money, time, effort, real estate (clutter) and frustration in recent years. I used to visit many so called high end stores, listen to the sales pitch, then multiple amps that got swapping in and out, pairing with different loudspeakers etc., in search for the "better" sound quality. Now, if I am in the market for something, say an amp or dac, I would just do my research and make my choice based on specs, bench test results, and all available publications that have credible technical information; and then in the end on all else being equal basis, I would make my choice after considering the cost, aesthetic, and physical aspects such as size and weight.
You said you had your theory, but are those theory totally scientific based, on proven scientific principles, and on logical, bottleneck analysis? For example, on all else being equal basis, separates are better than integrated devices such as integrated amps and AVRs, but that's (all else being equal) based on interference between parts and components, that may or may not be a factor in the end results depending on the design and implementation of each as there are many ways to mitigate such interference that would result in noise and distortions, and such has been shown in test results many times, such as RCA unbalanced outputs did better than XLR balance outputs on the same devices such as the Marantz AV10 and Anthem AVM90, both are flagship class AVPs.
Many forum people may tell you class G, class D, class H, class A, AB, AAB all sound different, but in the end it is bench test results that tell the truth. Yes there are obviously things not measured, but if our audio experts such as Gene, Amir, John Akinson who have been doing tests on audio devices for decades know something that would affect sound quality (audibly), then would have included such tests. Also, if there are something that could not even be tested/measured, then we are out of luck anyway because in that case if a device, such as you favored Arcam amp did well in such things that have not been, and could not be measured, then how the hack did the Arcam design/engineering team managed to come up with their design that would give it such a distinct "sound", that did not show up in know scientifically based metrics such as noise, distortions, and frequency response? Perhaps it was a random process then? At least that would make sense logically speaking, but if so, then we really have to depend on luck to a large extent to make our selection and as you know it will be very difficult to make such a choice relying on our ears/brains as there are so many factors including but not limited to the speakers paired with the amps, room, placement, even our mood at the time, that all affect our perception, let alone the various cables that those demo room reps do tend to believe and would try to sell you those things would make clearly audible differences.
You analogy based on cars, is a popular on on audio forums but again, as has been pointed out by many, so I won't repeat what's been said before, is not really relevant.
Sorry about my long post, I do this because it seems to me you are open to reasonable discussion on this controversial topic and I am interested in knowing why some obviously experienced audio hobbyist who seem knowledgeable, yet still seemed so convinced amps could sound so audibly different when all the measurements on metrics known to impact on audibly different sound quality show they should at best sound subtly different when used well below their rated output capabilities in terms of voltage and current. Note: I always prefer not using "power" to avoid arguments about impedance and phase angles etc.
Please feel free to ignore this long post, won't hurt my feelings at all.
