It's an extension board specifically for auzentech branded cards, not necessarily the prelude. It allows you to output sound through HDMI for use with a receiver that supports it.
I would imagine that the video input would accept any HDMI/DVI video signal, regardless of the source, and then multiplex it with the audio signal. Your video card wouldn't matter. Personally I would prefer the video and audio be on a separate path, so I won't be using that anyways (just run the audio directly to my receiver and video directly to my monitor.)
As well as 8ch LPCM, which would be better for games (you'd only use DTSHD and DTHD with movies.)