I don't know any specific about rio, but try to remember that most mp3 player do not issue linux drivers and are also unwilling to tell anybody else about how to *start* doing it (correct me if I'm wrong, I'd love to be).
Most mp3 player linux drivers are worked out in rather painstaking fashion using reverse engineering.
I have an iriver ifp, and for early firmwares, linux drivers had been worked out, but changes to firmware (i.e. UMS) now mean having to edit the linux kernel itself, which is no small job. I must say, it does not "mount" in the usual manner. Expect new ways of doing things in this context. Have you tried the man page for rioutils? Check out the source code for the readme file, you may get some clues there.
I'd do an exhaustive google search for these drivers and prepare to be disappointed. YOu may have done this already, you don't say. Good luck anyhow, I know I didn't help much, but it ain't that easy ...
Last edited by stabu; 08-12-2005 at 06:32 PM.