There is an MP3 player for an alternative Dreamcast OS called KOS.  I think
you can swap CDs, but I'm not sure, as I haven't tried it.

Full source code for the MP3 player, KOS 1.0.0, demos, games, and a lot of
other stuff, is provided in the DC Tonic package.

http://sourceforge.net/project/shownotes.php?group_id=23791&release_id=36074

http://sourceforge.net/project/showfiles.php?group_id=23791&release_id=36074

RC5Stint