What this does: controlling volume for deck 1 or deck 2 from any interface (midi controllers, GUI, or TouchOSC) results in midi output sent back to TouchOSC to update their positions
Note: I did this without reading https://github.com/mixxxdj/mixxx/wiki/midi%20scripting and I think the midi scripting interface probably resolves the issues I had and simplifies the approach.
A google of mixxx osc
turned my afternoon into this...
https://www.reddit.com/r/DJs/comments/rwq59j/djing_on_a_budget_homemade_touchosc_controller/