After carefully reviewing the manual and seaching this site/the web for too many hours, I was pretty much convinced that there was no simple MIDI controller assignment for selecting a Submix in Totalmix without succumbing to some variation the Mackie protocol, but then I stumbled on it mostly by accident.

Anyways, in case this isn't common knowledge, here it is in simple english:

MIDI channel 13, CC 104-116 selects Submix channels 1-12
MIDI channel 14, CC 102-106 selects Submix channels 13-16 + Phones

This should really be better documented! If it is well documented and I somehow missed it, I appologize for wasting space

Hope this helps save someone else from the frustration of not being able to do something that should be so easy.