XM Express Audio input/output discovery?

I just installed an XM Express tuner in my car, and just by chance, I plugged my MP3 player into the jack on the docking station marked "Audio Output." I know this is for connecting the Xpress unit to a car radio's "Accessory" input, but I was amazed to hear my MP3 coming through over the XM station I was tuned to.


I was looking for an exmpty XM channel/frequency, so that I can use it as a setting to listen to my MP3 via the Express but couldn't find one. Any ideas? Thanks.


Carl

Richmond, VA