Okay, I saw your equipment on the Virtual system list.
One thing that I see is that the AGD amps are only 85 watts and I think the Quads would appreciate a bit more power, especially for loud playing.
Second, is the Class D architecture of the amp. I have heard from some designers that Class D can 'smear' the signal- which might be what you are hearing.
As you have an Atma preamp, why not call Ralph Karsten and discuss what is happening. He knows a lot, and can give you some guidance that we mortals here on Audiogon can't. And, he has built his own Class D amp and should know what might be going on.
B