I'm no expert but it sure sounds to me like there is a problem with DC leakage from the 950. From what I have learned, if an amp makes the thump there is nothing that can be done to eliminate it. As far as why some amps do it and other don't based on design, I can't answer that. That's way over my non-electrical engineer head.

Anything new in this area?

Run a 2ch Audiosource amp for surrounds, a separate powered sub, and a B&K amp for the 3 front channels.
Being to think I have a problem because I never hear anything when switching inputs/modes.

No one ever figured this one out, ey?

My newer Rotel five channel amp = no thump. Odyssey two channel amp = no thump.
Chiro c-500 five channel amp = thump.

Tried the Chiro with two other processors (the one that comes with the Acoustic Energy Aego system (bedroom system) and a denon receiver being used as a processor. These combos = no thump.

Someone has to know somoething about this! Anyone?