Coax and Optical cable not co-oping!?

It sounds to me as though the surround system is considering both the optical audio and digital co-ax inputs to be the same. This may just be a configuration issue. For instance, on my receiver I can ign arbitrary jacks to arbitrary input names...and for some reason the factory default was to lump all my digital audio inputs together. Pretty stupid if you ask me... The fix was to ign my co-ax input to one name, and the optical audio to another. This way, the signals wouldn't conflict with one another, even if both devices were on.