Hi Sexysynth,
Congrats on your Roland JX-3P. Wonderful synth and same generation as the Junos, but with two DCOs per voice. A bit more difficult to edit the sounds without the PG-200 module, though.
There is an upgrade option from Kiwitechnics, the Kiwi-3P upgrade kit. Now, yours could have this upgrade installed... have you checked?
Please take a look at this link at the Kiwitechnics website. The original Roland JX-3P service manual is also available for download there. The svc manual will be very useful for you in any case, upgraded or not:
Good luck and keep us posted
Bo