The DSX and DS doesn't have optical out though strangely, only the DGX.
They do, but its shared with another port. The DS/DSX share the SPDIF output port with the Rear Speakers output port, and the DX shares the SPDIF out with the Mic Input port. ASUS did this to save space.http://event.asus.com/multimedia/xonar/find.htm
And yes, anything with Dolby Digital Live or DTS:Connect (DTS Neo: PC) would work.