My 2p's worth. I own both a class A and D amp. In the studio I can tell no difference what so ever between them, however when playing live, I find the volume in both to be of equal measure, but to my ears the class D amp sounds like it is lacking in depth, whereas the class A seems to have that in bucketloads, which I can actually both feel and hear onstage through my cabinet. This is with both EQ settings in similar configuration. Not exactly an answer with any scientific based rationale I know, but that just my playing/gigging experience of these amps, and I'm sure I tell the difference in a blind test.