Status update:
The M9 is a funny beast. If I send the CC for "Overdub" while IN looper mode, nothing happens. If I send "Overdub" when in Scene Select or FX Select mode, it works just fine. This is OK, as you'd never be IN looper mode while using an external MIDI controller to run the looper.
I've done some work on the user interface to eliminate some gratuitous buttons and switches, and here's what I have so far:
On power up, the controller tests its hardware, and lights each of its 6 LEDs in sequence. During this power-on test, hold down the footswitch for the mode you'd like to use.
Record - looper mode
Play - FX select mode
Play Once - FX select mode (reverse order)
Undo - Scene Select mode
Half Speed - Utility Mode
This setting is saved in the controller and persists even with the power turned off.
Looper Mode - just like the internal Looper mode, but the Undo and Play Once LEDs behave a little differently. If you need the LEDs to behave exactly as on the internal setting, use the controller in a different mode and use the M9 controls for looping
FX Select Mode - just like the internal mode. LEDs are smart and know who should be on or off.
FX Select Mode (reverse order) - the M9 is kind of dumb, and if you're in 3 > 2 > 1 order, you should use this mode to make sure the controller LEDs correspond to what is on the M9.
Scene Select Mode - selects the 6 scenes from Folder 1 only. If you need more folder access, see...
Utility Mode - allows selection of 4 scene folders (1 for each footswitch) plus Tap and Tuner.
You can chain together one or more of these controllers, and I can do custom controllers with a smaller subset of functionality. These controllers are also capable of sending MIDI CC / expression data using a standard volume pedal although lower-impedance passive pedals like the EB VPJr 25K are best for this.
I am trying to post a movie but here's something to tide you over until then: