After doing much research and testing it seems clear that the fuze+ (firmware 2.38.6) still is unable to read useful m3u playlists in MSC mode (such playlists only work if the listed songs are in the same directory as the playlist, i.e., any path component is not parsed/handled correctly by the fuze+).
However, I found that I can import m3u playlists into the gMTP program (native app under linux; I’m currently on ubuntu-10.11) and write them to the fuze+. That’s at least something, isn’t it?
gMTP issues a bunch of warnings (that the playlist cannot be updated - this happens when *reading* lists from the device). However, I just ignore the warnings and it seems to work fine. When I connect the fuze+ then it shows up in nautilus (MSC mode)
which is how I normally use it. When I issue ‘connect’ from gMTP then it automatically ejects the usb-storage device and connects in MTP mode - nice. Be patient, though: some operations (connecting, writing playlist) take a while…
FWIW: The first lines of an .m3u playlist (I found that when exporting an existing playlist from the fuze+ to gMTP and storing as ‘m3u’) show (<title> is the title of the playlist as it appears on the fuze+; regardless of the file name):
#GMTPPLA: <title>
Music/<Artist>/<Album>/<song>.mp3
