Actually this is a topic I too have been wondering about. When I built my HTPC I was thinking that I would need a separate audio card for decent sound out.
I would think/hope that if you are doing your decoding on the receiver, that you would be able to do passthrough of both audio and video using the same hdmi connection.
By the way, I have hdmi out on my amd690g based mobo graphics so I expect something in the ATI line of cards will have hdmi out.
I have no idea whether or not it will pass audio and video and what exactly it will pass. I need to read my documentation again, but last time through I didn't find it very helpful.
