Originally Posted by MowTin
I've learned the hard way that just because you see a digital or optical output doesn't mean you'll necessarily get 5.1 sound.
It wasn't intended for this to begin with. SPDIF was designed back in the late 80's for digital transfer from CD players to audio receivers, thus eliminating any analog interference. It was only intended for stereo 44.1khz 16-bit. However, the TOSLINK and coaxial connections are capable of going up to 96Khz 24-bit, and hardware that can support it will.
Dolby digital is able to output 5.1 audio by sending a lossy compressed digital bistream rather than a simple PCM signal. DTS works in a similar way but the format is different. Thus you will not get anything other than stereo to your receiver unless you can encode to one or the other.
That is why several cards these days support DDL and DTSi, which encode to DD or DTS in realtime, thus enabling surround in e.g. games as opposed to just watching DVD's.
Creative has maintained a stance that they basically hate both of them and will never support either. The only option they provide is to buy a separate box for $200 (ripoff) that you connect the analog cables to, and this then encodes a DTS signal from that to your receiver. But this still gives you the problems with an analog transfer, namely crosstalk and EMI inside of your computer case, and is ultimately pointless.