Some of you may already be aware of this, but I think it's still worh-mentioning:
This guy named Greg Baumont had the brilliant idea of developing a software application that emulates a PG-800, that is also capable of loading sysex to and from the JX-10 without requiring the M64-c.
It it a donatioware called GB-800 that runs on windows XP and requires the Colin Fraser ROM upgrade (which is totally recommended by me).
Ever since I started using it my tone-sharing conflicts ended, because it allows me to save every tone setting in my laptop without having to re-write the JX memory. The PG-800 functions are made redundant for those who own the real PG, except for the fact that one can assign any regular Midi controller to change the parameters (thanks to the Colin Fraser ROM).
Go for the "Downloads" section in the main menu.
Hope that helps.