I have connected my XM Radio to the Aux Input of my Outlaw receiver with RCA cables and it works fine, so I thought I would get a digital cable. One end to the XM radio is Mini plug, the other end to my Outlaw Receiver is a Optical Connector but I could not get any sound, even though I tried the digital selector switch. Below is the Monster cable I am trying to connect. any suggestions on why this is not working??

http://www.monstercable.com/home_av/audio_cables/digital_interconnects_tm.asp