Jason,
I experienced an odd very loud static-like sound (through the speakers) when my PRA-9X is in variable mode. I tried rearranging my gear because I initially thought it was wires and cables not getting along. Then, I moved my system into my tiny home office hoping that would solve the issue, but it persisted. Finally, I switched my preamp to 'fixed', and everything seems to be fine now. I control the volume either from my DAC's volume control or from my computer.
What is it about the preamp's variable setting that causes such interference? [I'm mystified.]
Michael