Glad that you got it all worked out. Background hum is the death of many. I spent a good 20+ hours trying many different things when I had the case of it. I eventually decided that I'd spent enough and it would have been cheaper to just buy new equipment than try and diagnose where the problem was coming from.

And now I have an Anthem AVM60 ;-)

Anthem: AVM60, Fosi DAC-Q5
Axiom: ADA1500, LFR1100 Actiive, QS8, EP500, M3, M3comp, M5