[slizzap]

Already ahead of you there. First thing I always do after I do the ATI CCC installation is open up the list of Playback Devices and configure the speakers for the HDMI output. Just like you said, by default it's set to stereo. I set that to 5.1 and run through the test tones. Everything works perfectly here. I usually configure the sound to 24-bit 96khz (studio quality), but I even took that back down to 16-bit 41khz...none of that really matters in this case anyways.

I think all the obvious stuff really is out of the way here. Tonight I'll be working on getting AC3/DTS passthrough working outside of XBMC to make sure it's working properly from the PC itself.

There is a separate Realtek ATI HDMI driver. Here's their download page (just click on the accept checkbox). It's the one highlighted in red. It's a Realtek driver specifically for the ATI cards with HDMI out.
http://www.realtek.com.tw/downloads/down...Down=false

I've always just been accustomed to using the Realtek driver over the ATI driver, since when I first built my HTPC (when the Radeon HD 3xxx series just came out) I think the ATI driver was completely broken...sound only worked over HDMI using the Realtek driver. Based on what I read recently It seems like there are pros and cons to using both, but they both now work.