This is my cabinet setup:
Frontend: Game Launcher
Arcade - MAME
NES - Virtual NES
SNES - ZSNES
GENESIS - GENS
TG16 - Magic Engine
LaserDisc - Daphne
You can run all those emulators from Game Launcher. They can all load games via the command line, so game launcher handles them fine. ZSNES, you can easily configure it to exit with the press of any button you want (except ESC...but there is some way to hack the ZSNES.EXE so you can exit with ESC...search the board...that solution is on here somewhere). Gens, unfortunately the only way to exit that emulator is to 'right' click the mouse while playing the game and choosing exit from the menu. TG16, no problem there. Virtual NES, no problem there (the absolute most configurable emulator I have ever seen by the way). Daphne, no problems.
So basically you choose your games through Game Launcher and it launches the appropriate emulator with command line commands and off you go. Can't help you with mp3's though.