The Audigy 2 cannot output anything more than 2.1 digital sound through the 3.5mm socket to anything other than Creative speakers.
The exception is where you configure a DVD movie player to use S/PDIF Passthrough and feed a signal from the coax or optical S/PDIF outputs (found on the Platinum and above versions) - the DVD's audio gets passed through the S/PDIF port.
There is no way to get a Creative card to encode and output real-time 5.1 digital audio on a single channel (eg, like Dolby or DTS).
I went over this (rather poorly, I must admit), on another thread. (either Soundblaster Digital or something else with a name like that)
[EDIT]
Sorry about confusing you in the other forum, Grayson. You cannot get Dolby Digital, or even S/PDIF Passthrough for DVD movies on the 3.5mm jack on SB Audigy (or in fact, any previous) cards.
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