I've had this problem for a long time, I generally have tried to ignore it but it's really gotten on my last nerves as of late as to WHAT the problem is. I am using an M-Audio Revolution 5.1 sound card, I have for years. My speakers are Logitech Z-5500 (Support DTS 96/24 and Dolby Digital PLII decoding). I'm always able to get surround out of games - but I'm beginning to wonder if I'm just getting matrix surround and not true surround.
In the Sound settings I have two devices shown - Speakers and then SPDIF Interface. I have my speakers connected via a Digital Coax cable and always have. This is the only cable I have connecting my speakers to my computer. The speakers are what is selected in my settings. If I tell it to use SPDIF out, the level meter next to it moves but I have no sound on the speakers. If I go into configuration for my speakers I get all the setups (Stereo, Quadraphonic, Surround, 3.1 Surround, 5.1 Surround [Side], and 5.1 Surround [Rear]). I can choose any of these, but as soon as I pick my setup (5.1 Surround [Rear]) and hit test I get this message:
If I say Yes, then I get this message:
The only mode that works is Stereo. If I select 5.1 Surround [Rear], and just hit next it lets me go through the setup wizard. When I hit finish though, I am greeted with this message:
But what's stupid, if I go under properties for SPDIF Interface and test the supported formats of DTS and Dobly Digital they work fine and my control pod switches to DTS and Dolby Digital respectively. But when playing games it never switches to any kind of Dolby Digital or anything like that. So what is the problem here, why can't I set my speakers to 5.1 in the Windows settings? Are my games actually in discrete surround sound or am I getting matrix surround for my games? Just a thought, but do I need to hook the analog portion of my sound card up to my speakers to get discrete surround for games (Because they don't support digital output)?
I've kind of always just imagined "Yeah I'm getting real surround sound" but now I'm not sure if I am. Any time I watch movies on my computer though I get all the real surround modes, the control pod switches over to DTS, Dobly Digital, etc. and I know I'm getting true surround. Is there something I'm not understanding about hookups or does it not matter what Windows says my speaker setup is? I have a real setup I plan to be swapping for this system soon (Onkyo TX-SR500 + Definitive ProSeries speakers) but I want to make sure I've got it all working the way it should. IIRC, most games are Dolby Digital and I know my control pod never switches to DD when I play any games - only movies. I know both my sound card and speakers support DD and DTS so I'm not sure where the problem lies. Most people reporting of issues getting Windows to go into 5.1 have crappy Realtek audio, not M-Audio so I'm not sure how this differs my issue.