Using the MIDI message functionalities is great to create custom setups or control of external gear, but alas it is not possible to manipulate channel-specific parameters as other channel-specific in-console parameters are manipulated: by selecting a channel and then using the respective controls (such as dynamics, filter, etc).
The channel-selection is available in the SQ Mixpad app which relies on the non-disclosed protocol, unfortunately.
This is a limitation of the possibilities at hand.
If the channel selection would be accessible as MIDI message then external setups can build upon the very same idea of thus manipulating channel-specific parameters using the custom rotaries etc.
A very small change with a rather big impact.