Obviously you are missing something on how to properly set up a bias controlled comparisons.
If that amp had all those issues, that would show up on the specs; you heard about specs? Can you tell us if the Fr on that amp is not flat at those bands you happen you have issues with? Or, maybe it is your speakers, your room acoustics, or your bias that is interfering?
And, that 28Hz thing. Perhaps you just don't understand that spec? How much spl can that speaker deliver with a 28Hz signal? Oh, maybe that is the issue, just not enough. And then you blame the amp.

And, just because you are a musician doesn't give you any better edge about audio, listening, etc. Oh, yes, that has been well demonstrated in proper controlled testing.