Follow up to my last reply:
I see now how you were confused. I looked at the link for the cable you purchased. Honest mistake!
It is an optical cable with a standard toslink at one end and a mini-optical plug at the other. The mini-optical is meant to be used with a portable mini-disk player or somthing of that nature.
The mini-optical is not the same as the analog 1/8" mini plug on the XM.
You might want to return the cable and get you money back.