Look for the MP3 Bulletin
Do a search in the 6er forum for "MP3 bulletin". Several pdf's available that indicate it will work for your car. Dealers don't want the liability to upgrade without charging $500 for the service on an "out of warrenty" item.
If you find a reason to make them do it, let me know. I want to up grade to play MP3's as well.
Be of good cheer.