I have a ATI Radeon 4550 HD graphics card with HDMI out. It does support sound, it definitely used to output in 5.1 surround just fine. I'm currently running Windows 7 and last night I installed the latest Realtek drivers
, then the Realtek HDMI drivers. I now have the option when I select my playback device for 5.1 surround but when I do the test.. my receiver still only shows a signal to output in stereo at 48hz. I then installed ffdshow, and well.. nothing still. It's getting quite frustrating.