My 2001 S4 needed one so ordered this and received today:
http://www.audipartssuperstore.com/catalog/product_info.php?cPath=309_305&products_id=971
I have an iPod adapter in place of the CD changer.
Now is the time to pick one up whether you need it or not.
http://www.audipartssuperstore.com/catalog/index.php?cPath=309&osCsid=3d0ec781nc7bfg9qb7qegb85f3
http://www.audipartssuperstore.com/catalog/product_info.php?cPath=309_305&products_id=971
I have an iPod adapter in place of the CD changer.
Now is the time to pick one up whether you need it or not.
http://www.audipartssuperstore.com/catalog/index.php?cPath=309&osCsid=3d0ec781nc7bfg9qb7qegb85f3