I made a quick video showing how to trick the ipad into using headphones and the op-z as an audio interface to record 16 midi tracks and a stereo audio track at once (I realize several tracks do not need to be recorded but just wanted as a proof of concept)
Record op-z into ipad with just usb-c transport midi for multitracking into cubasis or aum
Record screen in op-z app while running audio in background AUM
Add nucleum hub attached to ipad for op-z recording and after opening aum then plugging in headphones (usb-c headphone adapter) so the ipad recognizes the op-z as an audio interface 2 in 2 out but immediately after the headphones are plugged in the ipad recognizes both.Rec hub headphone quick tutorial