Look at the Shadow SH-075 - that is basically the external version of the electronics in your guitar. Designed by Andras Szalay (same guy who invented the Axon technology and the upcoming Fishman Triple Play).
Manual here:
http://www.shadow-electronics.com/doc/pro_pdf1/en-GB/SH_075_english.pdf. I bought one of these once, but just to cannibalise it for the pickup (to replace a broken pickup on a Roland GK-1, which were not available when I needed one). Before you ask - I'm not sure what happened to the rest of it - might have ended up being thrown out or tossed in with the boxes of stuff that other luthiers were given when I stopped repairing.
I would guess that - like all the Casio MGs - by now it would need recapping to get it to work (as with an amp, the electrolytic caps all start failing after 15-20 years). Otherwise, the external version is still on Shadow's site for EUR 590. To be honest, I'm not sure they still make it (but it wouldn't surprise me - Steve Morse still uses them), but even if not, it would likely be found lurking in someone's old stock somewhere or secondhand on e-Bay.
http://www.shadow-electronics.com/viewpro.html?id=165
Same story with the combined humbucker/hex pickup your Ibanez used - I can't remember the model number, but there is likely some dead stock somewhere. Tuerk/Turnkey were the agents - they might have something lurking (but don't expect them to know what it is they have if they have it, so approach them armed with model numbers).
A really good resource for all things MIDIguitar is the MIDIguitar Yahoo group, which includes such luminaries as Andras Szalay, Richard McClish (RMC), Harvey Starr, Les Fradkin, and all the old stalwarts of the MIDIguitar scene like Joel Christian. Between the group, we seem to know every single system ever released (there are even a few collectors!) and are an absolute mine of info, manuals, pics and parts.
http://launch.groups.yahoo.com/group/midiguitar/