To keep it all factory then all you have to do is find a usb radio, usb harness, and the usb plug. In my truck it has the plug in the console and I have seen others non LTZ trucks that have it in one of the cig lighter ports. I am not sure where it would be on Tahoe's and Yukon's. You would also have to program your Vin into the usb radio to get it unlocked, then your done. Also you don't have to get the OE usb harness any usb cord of the right length and style of plugs can be used. Also no need to worry about onstar as it does not effect anything for it.
Or get the Isimple kit isgm571 for the ipod for 189.95 or there tranzit usb IS32 for 89.95 for a more universal kit for most mp3 players and you also get to keep your XM radio with the ISGM571