Well, we added a settings screen in the app so you can select a MIDI device and send it to the H9.

It turned out to not be possible to have the app itself create a Core MIDI device so that you could send MIDI to the H9 from other apps.  The reason being that H9 Control can't run in the background.  The app connects to the H9 over Bluetooth, and if you try to let an app that uses Bluetooth run in the background, it leads to all kinds of problems.