I can't think of any explanation for what you heard with the Panamax, or how the Emotiva could possibly affect the sound of an amplifier in any audible way. It is possible that somehow these devices could limit current, but that wouldn't be so easily audible, since most listening is done at a few watts. Even if you were driving peaks of over one hundred watts per channel I'm at a loss to explain it, though you did claim to be able to clip AT3000 channels.
60Hz AC power at 120v just isn't very complicated, and once you hit the transformer, rectifiers, and smoothing caps in an amp most possible effects are long gone. Even if you do have significant DC offset on the waveforms it's not something that would change the sound of an amp, it only affects the transformer, which isn't really in the signal path.
I have no experience with either of these power protection products, but the idea that somehow they can make an amp sound less clean is very odd, not far off in my mind of someone claiming that there is a difference between power cords.