For the crashing, it should save the MIDI presets as it converts them, so you can try again and it will continue where it left off, and repeat until done.
For a newer iPad without a headphone jack, you can buy adapters that go from USB-C to 1/8" stereo, or that split from USB-C to 1/8" stereo and USB-C, so you can power the iPad while getting the audio.