optical cable

I want to connect my Behringer UCA222 to my Audio Pro A38 via optical. I can hear the source e.g cassette via headphones in the UCA222 with monitor on. On the A38 I have selected Optical and have a red led on the speaker. If I look down the optical cable I can see red light. But no sound...

Decided to check out Redbull TV but disappointed that it only plays in stereo. Is there a way around this? I did wonder if it's because I don't use ARC (annoyingly that never worked smoothly) and instead use an optical cable. Any ideas?