Not to insight a riot but more importantly just an observation. Looking at your equipment list I notice you have direct tv HD box. I really think that is your problem. I have a DTV hr10-250 and it has magor issues. I'm running the new firmware and yet i get no audio, hiss and pops all the time. It has alot to do with the source going from HD channels to regular channels, or switching source from say a dvd to watch tv. I have been wrestling with this issue from day 1.
I hope this helps I know how fustrating it can be spending big money (700 bucks is a 2 week salary for some) and not having said equipment work flawlessly.