Had to go to the manual and it states:
AUX Send Controls: These virtual rotary controls
can be used to adjust the level of the currently selected
channel that is sent to the corresponding AUX
mix. The Pre/Post buttons allow you to change the
corresponding sends from the channel from prefader,
pre-EQ, pre-dynamics and pre-fader to postfader,
post-EQ, post-dynamics, post-fader
Wasn't clear in the app.
From a work-flow aspect having all aux's and the main on the same layer is far better than Mackie's multilayer approach especially if your trying to control tops and sub separately. Of course you don't need to do that since you have matrix and groups available.