According to the USB specs, it is quite allowed for a "physical unit" to have several "logical interfaces"
My D-link cheap-cheap digital camera is both a digital camera and a digital video camera when connected to my laptop.

The ideal solution would (of course?) be that the empeg player has both an ethernet "emulation" and a storage device "emulation", that way, it could be mounted as a "harddisk" on quite a lot of OS platforms.
The "read file" for mp3 files work seems to have been done already by mlord. Writing mp3-files to this disc, and having them show up in the playlists may be trickier, but not too much...

(I wish I had more spare time to write cool projects like that)

Marius (Escort Cab + Mark II)