I bought a Creative DDTS-100, which I run my PS3, 360, PC, Wii and Digibox through to connect to my Gigaworks speakers.
It has built in Dolby Digital and DTS decoders and can take 3 optical sources as well as 3 analog, and has standard connections for PC speakers.
Great piece of kit, but extremely hard to track down in the UK for some reason.