If you want to control totalmix via midi you must read and follow the instructions in the User Manual! The entire answer to your question is in the User Manual starting on page 75. In my previous post I told you page 78 which is for the fireface 800 however in your last statement you indicated you are using the fireface UFX which has a differant User Manual. Therefore the page was incorrect for your application. So get your user manual turn to page 75 and begin reading for complete instructions.
Page 75 Fireface UFX Manual.
30. MIDI Remote Control
30.1 Overview
TotalMix can be remote controlled via MIDI. It is compatible to the widely spread Mackie Control
protocol, so TotalMix can be controlled with all hardware controllers supporting this standard.
Examples are the Mackie Control, Tascam US-2400 or Behringer BCF 2000.
Additionally, the stereo output faders (lowest row) which are set up as Main Out in the Control
Room section can also be controlled by the standard Control Change Volume via MIDI channel
1. With this, the main volume of the Fireface is controllable from nearly any MIDI equipped
hardware device.
MIDI Remote Control always operates in View Submix mode, even when the View Option Free
is currently selected in TotalMix FX.