Are you sure there isn't a little dongle in the box with the Audigy? That sounds like a proprietary connector. As for the RCA connector on the other end, since the signal is digital, all it is is 1s and 0s. You don't need more than two conductors for that!

Just to satisfy my own curiousity, what led you to post this question here? (not saying you shouldn't have, just curious)

I am the Doctor, and THIS... is my SPOON!