I've escalated this thread.
Just to add my two cents, I have a Mitsubishi 52 inch flat panel I bought about five years ago. I'm running hdmi to the tv from my SMP, and unless I play a video file first, I can't get sound on any of the services, including my favorite, Hulu. I found out that my tv doesn't really handle streaming sound over hdmi very well. But for some reason, once I play a file containing sound - even for only a second - the sound on the services work.
Right now I'm running stereo through the hdmi cable. I found digital wouldn't work at all. As soon as I can, I'm setting my surround sound back up, because I never had any problems when I was running sound through my sound system.