It is not that difficult…
I have the steinberg Midi in connected to my OT for sync Info.
The ipad is connected to the steinberg via lightning adapter.
Through that it can receive the midi and audio signal and can give the processed audio back to the steinberg.
The audio outs from the steinberg go back into my mixer in a dedicated channel.
Audio from the Mixer is sent via AUX(2 in my case) to the audio in of the steinberg…
In Turnado (for example) i assign the audio ins and outs of the steinberg and assigned the midi to receive my sync signal (for tempo and start / stop)
that is all and I can put whatever signal from the mixer aux to the ipad and can mix the processed signal through the channel in the mixer…
I guess this is quick and dirty how I do it but more than ok for me.