My Audigy 2 Platinum is connected out via Optical s/pdif to a Standalone Receiver or proper Speakers that have built-in 5.1 Decoders. and does light DD and DTS 5.1 Sound from the disk or file source. Linux has the Drivers for that Creative, so your good to go. How are you setup and what Linux Player are you using for the Playback?
Just connect and go into the Player Audio Preferences and select something like AC2/DTS S/PDIF Pass-through and restart Player and select your Source and all should work. I am not in here, unfortunately, but for just a few days from tme to time, which I do hope will improve very soon, but I'll try to check back soon for your reply. Good Luck.
Oh yes, I agree........DTS rules and now DTS-HD is already the Future.