Hi Zeetha,
I can imagine that they are not too eager to work on it. It is a bit of a beast to work on and is so old they would probably have trouble sourcing parts.
As a midi controller it would work fine. I often used it to control a korg i40m module with no problem and used it to control the kn6000 via midi if I wanted the weighted keys. I have a yamaha 9000pro now and again the PX7 works flawlessly as a midi controller.
I will root my scanner out (it is in a box somewhere) and will scan as much of the manual as I can for you. There is a whole section on the PX7's midi capabilities. You will have to give me a couple of days but I will do it as soon as I have some time.
Best to you
Tony W