No rear channel on speakers now

[Gunslinger08]

I just noticed that my rear channels weren't working in CS:S, so I tested them with the Creative software.. no output at all to the speakers. The card is giving output to the rear, because I can plug the from channel cable into the rear port and it gives me sound, but not vice versa. I can plug the rear speakers into the front outlets on the back of my sub, and they work. But the fronts don't work when plugged into the rear outlets. So it sounds like either the rear cable from my card to my sub is dead, or the amp has died for the rear channels. Any ideas on this one? I have Z-560s.