Hey, don't the high end sound cards like the platinum version of the Audigy 2 ZS and X-Fi (with all the bells & whistles that you install in a 5.25" drive bay) have a DD optical output?
It depends on what you're doing with it. If you're playing games, then no, even the new X-Fi cards will not output 5.1 over the digital connection. Appearently Creative would rather sell the encoder
If you're watching DVD movies, then yes, you will get Dolby Digital/DTS from the digital output.