If I run DVI -> HDMI from the HTPC to the receiver, then run HDMI -> DVI from the receiver to the Projector then I lose the audio right?
Correct, DVI does not carry audio signals
The DVI to HDMI from the HTPC to the receiver won't transmit an audio signal, so I would have to run a separate eighth inch to RCA Y-Cable into the receiver on a different input. Can you tell the receiver to get video from HDMI but run audio from a different input?
On some receivers you can. The 3808 will allow you to set up the input audio and video source for each input.
Does you HTPC not have optical or coax out on the soundcard or mobo? If it does I would use one of those for audio which is the only way to ge 5.1, the 5.1 soundtracks are only carried over digital feeds.
