Maybe this will help. Hope at least some of it will . . .
It's distantly related to Arlo's suggestion (1).
(if it sounds familiar, it may be because I posted an edition of "War and Peace" 2-1/2 years ago that mentioned this)
I'm working on coming out of "retirement" and my proposed rig is:
- iPad mini
- Roland RD-700NX on bottom (has MIDI IN, OUT 1, OUT 2, and THRU/OUT 3 5-pin jacks).
- Kurzweil PC3 on top (has MIDI IN, OUT, and THRU 5- pin jacks).
Both boards also have USB type B ports.
Connections:
- Lightning to camera adapter to USB MIDI (B) on the RD700NX.
(Here I have to confess I took a non-recommended but effective step, extending the lightning cord with a short garden-variety USB printer cable; but hey, it works!)
- 5-pin MIDI OUT 2 from the RD to 5-pin MIDI IN on the PC3.
(oddly, the "THRU" port didn't work)
Seems to work just fine so far.