Upgrading Factory Radio

I have a stock RDS cd player in my truck, and I've been eyeing some factory 6 disc changers on ebay. I guess my question is, I have xm and onstar, do I need any special hardware to exchange the radios. I know you need a code for the new radio. Anything that anyone knows about this would be helpful!!! Thanks

Got to xm411.com and ask "Ziggy" he is the owner of myradiostore.com and is very knowledgeable about these things.