Sounds like Will and I are in the same boat.

Mine is very simple. I have one level of hiss that comes from all 5 speakers. I can hear the center the easiest, probably due to speaker location, and the surrounds the least, certainly due to location/tweeter height. In a quiet house, I can hear it from 12' away.

If the 950 is powered up at a digital input, the muting circuitry in on, and it is dead quiet. Once the material starts, the hiss appears.

If the 950 is powered up at an analog input, there is the hiss. Switching to a digital input does not change the hiss. Analog bypass mode also does not change the hiss at all.