I don't use an iPad, but I have built a remote controller for the Harmonizers. I can't help you with your second question, but in answer to your first question, check out Eventide's Technical Note 98. It has the codes for the buttons…
As for MAX, do you know if it can talk to a serial port, or is it only MIDI-based? If it only communicates via MIDI, I think you'll be frustrated with the slow performance…
