I still think that running two 1/8 jacks into the single AUX RCA should work for two reasons. First, the receiver is what does the decoding, and is completely independent from the sound card. The receiver is what gets the signal, not sends it. Secondly, since the receiver gets both signals from the sound card, the information is going to the receiver, and maybe, just maybe, it will see that it's a surround signal. Both the sound card and the receiver are THX and DTS compatible, so hopefully it'll pick up on it.