Ive been trying to follow all this discussion across several threads. It seems that most people have the opinion that amplifiers shouldnt/dont make a difference.

I'd like to ask a question (Im talking about amplifiers here, not receivers that are made to change the sound with surround effects, etc)...

Considering that amplifier are rated by their manufacturers at % of total harmonic distortion. Isnt it logical to assume that they have tested to make sure that is the case?

A 0.07% THD would seem to mean that over the entire frequency range that the amplifier wouldnt change any input sent to it more than that amount. Are these ratings wrong/misleading?

If the ratings are correct, then is it possible for the human ear to hear that low of a distortion?