yes all the guts would be different, and most of the holes on the back would probably be different. The only thing I would be trying to line up is the 24 contact docking connector. Doing so would allow a slip in conversion for people with empeg or rio car players.

What inspired this is this line of MP3 chips from ATMEL along with their USB on the go chip sets, and a buntch of other stuff. This would be an ultra low buck player that only supports MP3 files. There are also one chip solutions for AM, FM, DAB, and DRM radio here

another more powerful option is a more empeg like player based on off the shelf laptop PC parts.