The ideal custom controller for me would be ableton and any hunk of crap controller with buttons or faders or whatever your looking for. hell you could program the control changes in midi ox if you had to.
What are you trying to accomplish with midi control??
Not planning on building anything, i was thinking (aloud) that maybe a generic/traditional midi mixer or gridbase controller are not the best UI for the octatrack?
I even fantasize about a kind of midi knobby battery powered dock. OT in te bed or on the go with a set of small set of faders/knows. I’m not an engineer, i think it shows : D