I don't see the coax out thingy you were talking about.
Are you sure I can do what you said with the sound blaster audigy cards??
Yes, I am positive. In one of my first posts I mention that you need to get a RCA to Mono adapter like:
It doesn't need to be right angled. It has to be mono like the one in the picture because it will be sending one bit-stream of information to the receiver.
The socket you want to use on the Audigy is labeled "Digital Output or -> 3". It is the one furthest from the firewire port. Plug the Mono adapter into it. Then, Plug a 75 oHM Digital Coax cable into the adapter that you just inserted into the card. Finally take that cable and plug it into the Digital Co-ax input on the receiver.
Finally on the PC open Creative's AudioHQ and select "Mixer" open the advanced properties tab, select speakers and make sure it looks like the attached screen shot.
You want to make sure that Digital Output is checked.