1. Snes is good, not complete yet though, most games play well without sound. And some games play great with sound. Depends on what game you want to play
2. Genesis to me is not good yet, no sound, FGen beta is the only good emu out there and it has not been made pulic, still no sound though
3. So far you cannot run an emu and listen to mp3 at the same. Would be nice if Opensnes had an mp3 player option but it would probably slow it down to unplayable levels.