Well, this discussion has about as much likelihood of getting resolved as vinyl versus cd, Bose versus whoever… Opinions easily become fact.

The only thing I can tell you is that we had a stereo store with sound rooms, and amplifier/speaker switch boxes.

If the source was identical, and amplifiers were volume matched, a client could not tell the difference between one amplifier and another in A/B testing, feeding the same set of speakers. Volume of course depends on power output, but we are talking about a sonic signature.

Speakers, on the other hand, produced dramatic differences in sound.

I have heard for years that certain brands had a thin sound, others were fuller or warmer… My personal claim is that if you unplug an amplifier and have another one in its place in a half hour, you don’t have the reference needed for a true A/B test.

Blind A/B testing sifts out opinions in a hurry.

Nowadays you can Audyssey or whatever most A/V receivers. At that point they are not flat, so yes you may have differences. Amps set to flat are very neutral.

We sold both new and used equipment over a 30 year span. So there is not a brand on the planet that I have not heard.

Nonetheless, like every other audio debate, it will never truly be settled. All I can give you is my anecdotal information and leave it there.