Its been talked about a lot, but we really don't have one setup to work with rockbox. The closest thing is Toni's emulator, which actually emulates the entire Sandisk Sansa, but only imperfectly. Its on the tracker, and I've proposed improving it as a possible GSOC2008 project.
If you come up with a good way to run ARM code (perhaps using an emulated ARM linux environment), I'd actually be very interested in looking at it.