.pla files are created by WMP et al when in MTP mode, yes, but the Fuze doesn’t care which mode it’s in when reading files 
You can use m3u, and they do have to be created in MSC mode, but they cannot reference both drives in one playlist - you have to use relative paths and put the playlist on one drive or the other, with only files on that drive being in the playlist.
.pla can reference files from either drive.
D.
