I also want to say I have never heard a difference in amp sound.
I recall back in the early days when I was a fresh young audiophile. I read about how amps and cables differ in SQ. I believed it too. But then I compared them for myself (volume match closely). And I said "WTF are they talking about! I can't hear any difference with any amps, AVR, pre-pro in direct mode!"
The only difference I heard was the volume. Some had higher gain and that made the volume louder. But when I level matched and the volume was equal, there was no difference in SQ.
I thought I was the only one who could not hear the difference. Then I read The Audio Critic and they had Electrical Engineers and PhDs and other established audiophiles who thought the same and double-blinded studies to prove that we just can't statistically hear the difference.
Now, okay, some amps are more "bad a$$" and built like tanks than others. ATI make amps that don't even have speaker hiss noise when you place your ears on the tweeter. Emotiva, Crown, Acurus, and all amps I've heard had hiss noise (noise floor). But from 6" - 12" away, as long as can't hear the hissing, so what?
But, most likely you won't need any amps.
Another thing is the gain level. Some preamp & amp (AVR) may have the gain level too low and it may prevent the amp from full capacity power.
So try this experiment. Increase the speaker channel levels in your AVR like from 0.0 to + 3.0 (Max is usually +12.0) and see if you can hear the difference.
A lot of people use room correction EQ like Audyssey, ARC, EzQ, etc, which may decrease the channel levels to like -3.0.
DenPureSound's Denon 4311 set his speakers level to like -5.0. So he complained he could not get the volume high enough. So I told him to manually increase the channel levels. He is 100% happy now.