I’m very glad to create the 100th thread of Gig Performer in Action! 
PianoArc is manufacturer of custom and exotic keyboards. They have a creative and talented team of people such as Eric Netherland and Brockett Parsons, keyboardist for Lady Gaga. Click here to learn more about the PianoArc team.
Here is a photo with Gig Performer:
–
I reached out to these guys to get more information about this setup regarding the Circle keyboard at Synthplex, and here is their reply:
The circle is comprised of 4 physical sections of 72 keys. However, in firmware the presets can be split up to 16 channels/sections in any configuration desired.
For Synthplex I believe Dave had it set to 3 splits of 96 keys each.
There is one physical USB MIDI input to the Mac laptop from the circle.
So in Gig Performer we simply needed 3 channels routed to plugins.
3 Instances of MIDI input receiving PianoArc. Each set to a separate channel corresponding to the splits.
Each instance then routed to a plugin (Keyscape, Roland Vintage, or PianoTeq)
Then all routed to the one audio output interface. Prosonus 1818.
The wiring graphic makes this very intuitive.Additionally, Dave was showing his narrow keys keyboard which was also plugged in via USB and routed to plugins in the same rackspace with a 4th MIDI input.
Audio outputs were simultaneously routed to the headphone output as well as main speakers.
Make sure to check them out 
Long live Gig Performer!