"Z, because it's the letter used in "Z80," which is the audio processor in a Sega Genesis."
YOU SIR, ARE AN EPIC WIN. You should also check out a Sound Driver/Audio Processor called Echo. It was created recently for the Sega Genesis/Megadrive. It allows the three PSG channels of the game system to play Commodore 64 Instruments, if my memory is correct.
http://www.segaretro.org/Echo