Ok....I think you are getting a bit confused as to what Dolby Digital is...
DVDs are a totally digital media, and so audio has to be stored in a Digital format. They also decided that they wanted 5.1 channels. There are a couple of digital formats that do this...they chose one of the 5.1 channel compression schemes called Dolby Digital (another common one is DTS, and it behaves exactly the same as DD, it's just a different compression scheme...like Zip vs Rar for computer data, exact same functionality). Then you pass this digital stream off to a device somewhere that converts it into 6 analog channels and sends it to your speakers.
You can not hear digital sound, only analog. It has to get converted somewhere.
Creative advertises that their drivers can do it...if the card detects a Dolby Digital stream it will split it into 6 analog channels and output (exactly the same thing an expensive decoder will do).
But what Creative doesn't tell you is that this is a pretty much useless feature. Either of the good software DVD players (WinDVD2000 and PowerDVD) can read a Dolby Digital audio stream and split it to 6 analog channels and send the 6 analog channels to your soundcard for output.
The only way Creative's drivers doing it are useful is if your DVD player doesn't support 6 channel analog output...and lets face it if you are ponying up $400US for some 6 channel speakers you can afford a decent DVD player that will output in 6 channels.
Creative's card doesn't even do it, the CPU does. It's just a driver hack, it's exactly the same thing as the way the software decoder does it.
Bottom line:
There is no soundcard that can do Dolby Digital decoding in hardware (the Aureal SQ3500 was going to, but it never made it to market) and ANY soundcard can do software Dolby Dgiital decoding in software with a good software DVD player.
As for Dolby Digital in other uses, no there are none. Why would a game use it? The game can just output directly to 6 analog channels if it wants to make use of them. Encoding to Dolby Digital would take more CPU time than appling effects like A3D, S3D or EAX....and then you'd have this Dolby Digital stream that you have decode somewhere and most computer speakers don't have decoders onboard, so it would fall to your CPU to decode it. So basically you would waste CPU encoding the DD stream, then you'd waste CPU decoding it so your sound card could output it to your speakers. Sounds useful huh?
At somepoint when we have really fast CPUs they might do it, because they you could hook up a digital passthrough to a home theatre setup and get surround sound from it.....but at the moment no (you can actually do this anyways, you just need a reciever that supports 6 analog "pre-decoded" inputs).
Real Time Dolby Digital Encoding would suck ALOT of CPU time. And I don't think it's that desireable for games.
Now there is a game or two now that support 5.1 analog channels, and there will be more to come I think. The next revision of EAX is going to support 5.1 channels, and I think S3D does as well. I know QSound3D does (On the Philips *Edge series)....but supporting 5.1 channels != Dolby Digital. Dolby Digital is a way of compressing 5.1 channels into one digital stream so you can connect your DVD player to your reciever with one cable, and save space on the DVD. It's not something that is desirable or useful for gaming, which can just send it's 6 channels directly through the soundcard, no need for compression.
I hope you can make some sense of all that.
atwl
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