I don't think many, If any games directly output dolby digital or DTS which would make the most out of your optical connection.
If you can live without the latest EAX I would choose one of the Auzentech's cards as they can perform real time digital encoding. I have the Meridian which seems to be discontinued?? but the Explosion would suit your needs.
The Prelude does EAX5 and has just come out but I am not sure if you would get that over the optical connection, and real time digital encoding will only be available at a later date.
Good luck