I have an ASUS P7P55D LE motherboard with onboard sound and I am running Windows 7 64-bit, and I am using the SPDIF output from my motherboard to my receiver. On my receiver I can see which audio channels are in use (i.e. stereo or 5.1)
In the audio interface properties I can test DTS Audio and Dolby Digital outputs and both work fine, but when I try to play a game with 5.1 sound (I've tried Left 4 Dead and Dragon Age Origins) it reverts to stereo. I was getting this behaviour with the default Microsoft drivers so I installed the latest from the ASUS website but there is no difference.
I notice that in the Advanced tab of the playback device Properties dialog (accessed by selecting the device in the Playback Devices window in Windows 7 and clicking Properties) the Default Format only allows me to choose from various 2 channel formats so maybe that is something to do with it?
I also notice that in the Playback Devices dialog I can press the "Configure" button when I select the "Speakers" device (which is the analog output) and in the "Speaker Setup" dialog that then opens I can choose from Stereo/Quadraphonic/5.1 Surround (which I have selected) and 7.1 Surround. However, the "Speaker Setup" dialog only contains the Stereo option for the HDMI output, and for the SPDIF output (which is the one I want to use) the Configure button is disabled altogether!
When I look at the audio settings in a game the Speaker Configuration is shown as "Desktop stereo speakers" which reminds me of the audio settings in previous versions of Windows.
How can I get 5.1 output all of the time?