As described in Babyface FS manual, section 24.5 (page 71), a MIDI Controller can be used to control TotalMix. It works great.  I use some switches and rotary encoder hooked up to a MIDI Expression to load snapshots and set the volume of my headphone output.

One small annoyance, however, if that TotalMix neglects to send MIDI feedback for the controls defined in section 24.5, in particular the Control Change messages for when you adjust faders with your mouse or the master volume with the rotary encoder in the BabyFace itself.  It does send Machie Protocol messages, but not feedback for the Control Change messages defined in section 24.5.

It's a small inconvenience, but I know how particular RME is with getting the details right, so I thought I would mention it here.