I've just successfully added MDX/PDX playback to modizer, based on mdxplay. Sharp X68000 was famous in japan and almost unknown in the rest of the world! It is really a pity for such a nice machine, check the wiki entry if you want to know more.
Regarding the sound part, it is based on FM synthesis + PCM channels and it sounds really nice. I'll try to upload a video later, meanwhile check this youtube video of another player for iphone.