I am almost done with the MP3 player. It can already process an m3u file and cycle through them. The occasional soundfiles simply interrupt them pretty much the way you described. The big issue is user interface. I think we can have a simple version quite soon... I'll talk to deniska about it...
( At the moment I am working on a GPSFS optimizer for Windows; it evaluates the GPSFS, can recompress the tiles and you can choose to omit given levels... I hope to release it in about 2 weeks, than I can focus on the MP3 again... )