One thing to be aware of is that the Creative card won't output more than 2.1 digital sound with this method to anything other than Creative's own speakers. I discussed this more completely (and somewhat unclearly, I must admit) in another thread in this topic (Soundblaster Digital, I believe).
If you want to have full surround, then use the optical or standard phono digital outputs (only on the platinum or platinum ex, I think) and set your DVD player software to S/PDIF passthrough. Even with this, you will only get sound from DVD movies.
I wish that Creative had put real-time Dolby encoding into their cards, like NVidia did with their motherboard sound chipset.