A "real" separation of dialogue, music and sfx isn't possible, although sometimes it works by taking only the rear surround-channels, which are only used for music and sfx. Unfortunately with Star Wars being the SFX-movies they are, you're always gonna have sound effects in there too. People did it, but the results aren't that satisfying.

Quality- and editing-wise I would prefer building the music tracks from the existing recordings (I guess the 3 2-disc sets of the SE-soundtracks and the 4-disc "Soundtrack Anthology" should contain all material necessary). I suppose that's what the creator of the ISOMIX-set did.

I don't have that set, but if someone could demux those tracks from the discs and upload them somewhere (yousendit.com, megaupload.com, rapidshare.com) they could be spread a little better (and get torrented eventually)