I am thinking speakers are a bigger point of interest than amps. The SR6011 has good specs and I would expect it to be clean at low levels.
However, I have definitely heard speakers that sounded very poor at low levels then came into their own once you opened them up. I expect selecting the right speaker will be the most relevant choice in getting this right!
I don't know what characteristics would affect this in a speaker, but someone else probably does. I do know that having the speakers close for low level listening seems to give a fuller sound.
How low is your low level? Do you have a SPL meter?