Aha - thanks for this.
At last, starting to get some helpful information.
So, this is a single instrument, an organ, with three keyboards (as large organs do have). The system assigns part of the range to one channel, other parts to another channel. This I understand is usual for organs, I've certainly heard of this before in earlier discussions.
So, we need to focus on Organ manufacturers. Maybe even Mfgs of organ kits, aspects of this sound at least slightly 'home-made'. This is not be disparaging in any way, a significant organ would be a large beast and a home-made option would save a massive amount of cost, not least in transportation.
I had a discussion with someone else a year or two back, he was trying to sort some problems with an organ. There was a question there (among other things) regarding channels, but along the way I think I remember his saying something about the inside electronics being Roland sourced, i.e. the maker of his organ bought in the tech bits as OEM supplier from Roland. I think his organ was made by something like Rogers - I'll have to try to track down the previous discussion.
Photo 2 shows a designation on the PCB 'MIDI 8709' - this may be significant. I've checked via the web but this info does not go anywhere. I'm sure however that there must be other info on the boards, maybe hidden by wiring (or dust ?). Even any info, or designations, on the keyboards would be a help.