Just to add to what ScooterMAC said, I only have one mp3 (arcade83.mp3) and when it's done, it's done. I have to restart mamewah completely if I want it to start again. (well, I've never tried the "next track" function)
Also, unrelated to sound, if I run MAME, I can't get NES, SNES, or Genesis (the only other emus I have in mamewah) to work. If I restart Mamewah and go straight to the consoles, they work fine, but if I use MAME, they stop working. This happened in both b13 and the final.
EDIT: Oh, and if I try to launch any emulator other than MAME after MAME has been used, it crashes to windows after a few seconds.