Let me get this straight - you're trying to use the "Digital Audio Out" on your Audigy, and are trying to plug it into how many RCA jacks? Are you separating the signal into right and left, or are you just piping the 1/8" mini jack to a single RCA jack?
It's just a bit-stream, so I believe that you must use a mono (only one end on the RCA end) and it should work. If you purchase a "Digital Connector" it will probably set you back $20-$40, and it is exactly the same thing.
I've been foolish enough in the past to buy a SPIDF cable to run from my DVD-ROM to my soundcard. It's just a simple two wire cable. I should have chopped a regular audio cable in half and it would have done the same thing.
Mono should work for the bitstream, but it must only have one connector on each end.