I think it only came out for the Mark III in Japan. Pretty sure it never came out in the west. It mounted on the top left of the Mark III and connected with a big SCSI ribbon that plugged into the front, and a smaller cable (power?) that plugged into a port on the back. I've only heard it emulated but it cranked out some nice sound for the era. Not sure if that tells you anything you didn't already know.
