The upgrade to the radio is a Aux Input Mod. There are instructions here on the site if you want to be brave with a soldering iron and the inside of the radio. Or you can send it to Sierra and they will do it for you. If I remember right it is about a hundred or so to have them do it. I had them do mine and replaced all the lights at the same time.
BOTTOM LINE: This gives you a cord to plug into a MP3 player and a switch between the player and radio. You can load a ton of CD's on a very small player. I got about 500 songs on mine. use Velcro to keep it next to the ignition switch. It will play all day on one charge.
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Make sure you check out the Wild Rhino thread on the event page, a group of semi literate GW riders in Kansas, Missouri, Nebraska, Oklahoma, New Mexico, Canada, Ireland, and lots of other places. Great group of people. Look to meet up on their next ride?? Perhaps think of going to NASSIR6 in July.