I tried searching using the search field at the top of the page but I seem to only get hits on Articles not forum threads. :-(
I recently upgraded my "old" P5W DH Delux to a not as old Maximus II Formula with the SupremeFX riser card. I used to be able to use 5.1 DolbyDigital over HDMI on my Gf9800GTX+ card and the little extra cable. I am using the 184.108.40.20600 driver on Win7 x64 and in the setttings for the SoundMAX integrated Digital HD Audio device it tells me that "only 2 channels supported" and refuses to let me choos anything but 2.0 stereo.
The bloated "Creative interface" supplied by Asus only affects the analog and SPDIF outputs, but these seems to be working as expected.
Any suggestion beside the obvious "buy a real sound card"?
Okay, I have more or less sorted it out. Here are a few good things to know about the "SupremeFX" shipped with the Maximus II Formula and "digital" sound in general.
1) The SupremeFX X-Fi sound solution may look flashy and use grand names, but it is cheapest of the cheap with little to no hardware to back it up.
2) The ability to output "randomly generated sounds" from e.g. games, web radio, Winamp or windows media player as a 5.1 Dolby Digital signal requires a hardware layer to encode the otherwise analogue signal to DD. One example of such a feature is "Dolby Digital Live", alas such features are not supported by the SoundMAX SupremeFX X-Fi.
3) Already encoded 5.1 Dolby Digital signals can be routed through the S/PDIF from e.g. a DVD-movie via a correctly setup Media player at the cost of "loosing" any other active audio streams. Meaning you will only hear the sound from the movie, not alerts from MSN, windows alerts or any other music playing simultaneously.
4) Contra intuitively, to have 5.1 Dolby Digital over internal S/PDIF and GFX card, the default output sound device in windows should be set to "speakers" not " S/PDIF Interface".
5) VLC (VideoLAN) can be persuaded to output a compatible signal from e.g. a x264 .mkv, if encoded correctly, by choosing the audio device "A/52 over S/PDIF". If this results in stuttering audio, change the advanced output setting under preferences to "Win32 waveOut extension output", restart VLC and try again.
6) Not all soundcards has an internal S/PDIF output. E.g. Asus Xonar DX, while an affordable and competent card sporting among other things Dolby Digital Live, does NOT have such a connector. Meaning you will not be able to output sound through your graphics card and HDMI using this card.
7) Soundcards and sound drivers were a big hassle back in the 90s but with the nforce chipsets and the following chipsets we (at least I) forgot how tedious trouble shooting sound can be. Do not take Your sound for granted because "one day the music dies".