To answer your question regarding who makes the instrument defenition lists for a particular keyboard, it is the software manufacturer who would do this. However, sometimes you can find a person on the web who owns the same keyboard, and they have already done one and they will share it.
Also, when Yamaha shipped out the first S80 to each dealer (demo model) there was a smart media disk installed in this unit. On the smart disk is a bank of sounds called GM, and you can load these into your S80. I would suggest you contact the dealer you bought this from and find if he could make you a copy by loading these in and then saving them on a new smart media disk.
George Kaye
Kaye's Music Scene
Reseda, California