Could I connect the Switch 3 to the H9 midi via a TRS to MIDI cable like this? http://www.disasterareaamps.com/shop/trs_to_midi_cable
It looks to me as if this only works with a few of their products – it is just an adaptor cable, not actually a TRS to MIDI cable. So that would be a no.
I've been seeing a lot of USB type B MIDI controllers on the market. Is there any way to interface those devices directly with the H9?
Not quite sure what you mean, You can plug a USB MIDI thingy into a computer USB, and then connect the DIN to an H9. What you can't do is connect the USB end to the H9 and then use it as a MIDI controller (wrong type of USB port).
It sounds like the best answer to your needs is to get a MIDI expression pedal (or a MIDI expression pedal controller) and then use a regular 3 button switch for the AUX. Note that most H9's do not supply power over MIDI.
