your motherboard, and for that matter, processor and memory, have little to do with bitstreaming. that's all done by, at least in your case, the video card. if your card is working with your current setup, that is, you can successfully test the hdmi sound output through sound manager, than everything is, theoretically, in place for bitstreaming to work. it just seems like, in these "early" days of htpc bitstreaming through video cards, all your stars need to be aligned for it to work correctly.
did you try what i suggested in my previous post? "kind of fixed" means another part of the system wasn't working correctly, so i replaced the whole system.