Sky, welcome. Yes, the situation you described isn't unusual, but you had the wrong target. If most of the source material sounds fine, then obviously the amplifier and speakers are doing their job well. The problem is with some poorly-recorded source material which good equipment reveals clearly.
A new amplifier can't solve the problem(you might want one for different reasons, but that's beside the point). Using the treble tone control can help, or the different treble curves that some processing, such as Audyssey, has available. A "warm" sounding amplifier would be either incompetently designed or defective; an amplifier should have no "sound".
