There seems to be a lot of confusion in here about this, and a lot of incorrect information about windows, video cards, hdmi & spdif. I have been running a HTPC (home theater PC) as my primary entertainment box hooked to my TV for a few years now. After dealing with issues like this for a while now, I've got a good handle on things at this point.
The short answer for the OP is to reliably get 5.1 audio out of games, you need to be using Linear PCM. Games do NOT do bitstreaming, which is what you must use if you are using SPDIF and want 5.1 sound. You need to either upgrade to use HDMI and use Linear PCM (simpler), or get a sound card capable of Dolby Digital Live to do on the fly compression and bitstream the audio over your SPDIF connection.
All essentially perfectly accurate....
My story:
Initially when I first started out I had an optical SPDIF connection going to my reciever. Since the OP said he is using SPDIF for his audio, I'll give you the definitive answer for what you can and cannot do with that sort of connection.
SPDIF can handle either 2 channel Linear PCM audio, or it can bitstream an encoded/compressed DTS or Dolby 5.1 signal.
I experienced the frustration with this long ago with a reciever that did not have HDMI inputs, only SPDIF. This is common with Home Theater in a box type setups as they frequently do not have HDMI inputs. When I had this setup, my games never produced surround sound, always 2 channel. Even with the exclusive mode enabled, it never worked. Now there are some games that are capable of using exclusive mode to send encoded DD, but they are rare. The vast majority of PC games have 5.1 or 7.1 sound but the games themselves do NOT do on the fly Dolby Digital encoding. Why that is I'm not sure, but the fact of the matter is they don't. My guess is the game producer would have to pay a license fee to Dolby Labs or DTS to be allowed to encode their sound in the compressed format, so they don't have an incentive to do it.
Precisely, It's unfortunate, and i really don't understand why as there are other digital 5.1-7.1 formats out there that don't require a license/fee to use and are open to anyone, but no receiver manufacturer seems to want to slap a simple decoder chip in there products. Pretty irritating.
Plus even for the low cost of the fee to include direct DTS/DD output formats from the game encoded BY the game and allow passthrough is also very frustrating. It's really NOT all that difficult... but oh well..
If I was going to stick with SPDIF my only option was to add a sound card like the Asus Xonar HDAV 1.3 or a Creative Labs card with Dolby Digital Live encoding, and this is currently the only option for the OP to get 5.1 sound over SPDIF. Some motherboards and Realtek audio drivers came with a solution that claimed to do Dolby Digital Live emulation, but I could never get any of these to work. I think they only ever worked in 32 bit Windows XP, nothing I found from Realtek did DD-Live under Vista or Windows 7 x64.
Eventually I got frustrated enough with the limitations of the home theater in a box and the SPDIF connection that I upgraded to a real home theater receiver with HDMI inputs. But that wasn't the whole solution either. As someone else posted, the earlier nVidia & ATI cards with HDMI output did offer "sound" over HDMI, but it was actually just SPDIF sent via a 2 wire cable you ran from an SPDIF header on your motherboard to the video card, then the SPDIF signal was passed over HDMI. So I was still stuck with 2-channel audio in games.
It is indeed the only viable option for the OP currently, but realtek shouldn't be excluded. Actually my experience, being a HTPC builder myself specializing in it and numerous other computer/electronics, building peoples theater systems with various formats and tech. My experience is opposite, with windows XP being the biggest pain in the ass to get it to output properly through a digital format of choice in anything more than 2 channel PCM. Even HDMI out from an XP machine is hair ripping torture. In the case of vista and win7 and windows 8, it's as simple as installing windows, installing the latest realtek drivers, followed by going into the sound devices in the windows control panel, picking the audio device you want to use, and then going into it's properties and selecting 5.1 mode as it's sample format. Apply the settings and done, Don't even need to use the realtek control panel, but alternatively using it to set the sample format has always been flawless for me.
There is only one downfall however, and it's relatively minor since most people don't run past the 48khz 16bit audio format, in EVERY DD/DTS sound card be it asus/creative/realtek, selecting it output correctly, but is only in a 48khz/16bit format according to even the latest home amplifiers.
No big deal, i'll take true 5.1 digital audio over 2 channel 96/192khz 24 bit audio formats.
Asus came out with the Xonar HDAV cards specifically to address this deficiency with the video cards. With the Xonar you pass the HDMI video signal through the sound card, then the sound card adds the full uncompressed Linear 5.1 signal to HDMI, or, since Asus paid DTS & Dolby for the rights to encode, a compressed audio signal if that's what you wanted. But this card was expensive.
About two years ago ATI/AMD came out with the 5xxx series of cards that were fully capable of 7.1 uncompressed linear PCM audio. Shortly after nVidia added proper LPCM audio to their 4xx series of cards. These cards will all bitstream, but only if the source has already been encoded (from a DVD or Blu-Ray). Their sound drivers will not do on-the-fly encoding, because why bother doing that with an HDMI connection.
So to the OP, you have two options
1.) Get an Asus Xonar HDAV or a Creative Labs X-fi Titanium and configure it to do Dolby Digital Live encoding over SPDIF,
2.) Upgrade your home theater receiver to one with HDMI inputs and use LPCM, and possibly upgrade your video card if it's not at least a nVidia 4xx or ATI 5xxx series card.
If you want to stick with your receiver, I'd suggest the Creative Labs X-fi Titanium since that does the DD Live encoding over SPDIF. I'd skip the Asus Xonar since, at $200, you're already in entry level home theater receiver territory. Secondly, they're harder to find now as well because, since all recent video cards with HDMI output already do full 7.1 sound, nobody is buying them.
Ideally though you should upgrade the home theater and use HDMI inputs, especially if you've got a fairly current video card already.
I've had numerous HTCP setups with creative adapters that would just flake out and result in bad things happening.. or lack of good things i should say.... i just utterly despise creative for their terrible driver/products, more failures then i care for. Asus's solution works relatively well, i've only encountered a few situations where it can svck due to hdmi lag introduced by using it's method of injecting audio into the existing video feed.
Otherwise I'm still mostly building system that have the least amount of issues with realtek audio solution on a motherboard outputting through the coax/fiber..... and now with the NEW HDMI output capabilities of realtek, lossless 7.1 channel output over HDMI directly from the motherboard to the amp with zero interaction with the video card. Flawless results so far.
Posted: Mon May 28, 2012 3:29 pm