No, no, no! Here's the right method...
The digital output from the SB card is on a mono 1/8" jack. Therefore, you need a mono 1/8" to single RCA adapter like
this. (Actually, you might be able to do it with a stereo cable. If you have one it won't hurt to try. But I know that the mono adapter will work.).
Plug that in, then run any RCA cable from that to the digital input on your receiver.
You don't need a special adapter.
You don't want to run analog to your receiver.
I have done exactly what you describe using an SB card with a digital output on a 1/8" jack, and I used the type of connection I linked above.
Good luck!