I guess that your main problem is that the selection commands are relative.
mesns: the same midi command can e.g. control the input level acting on output 4 or 7, depending on whether output 4 or 7 was selected before. This makes the midi command sequences in Cantabile difficult to handle.
I faced the same problem and first solved it with an Arduino. But in the long run this is impractical.
Since I had more ADAT I/O available than I needed with the Digiface USB and the Fireface UFXII, I solved the issue by connecting one of the unused ADAT ins to an unused ADAT out with an optical link cable.
This sounds absurd at first sight, but only until you realize that you actually have a whole matrix of faders in front of you. I’ll try to illustrate this with an example:
Suppose I want to control the volume of a synth at input 5 to output 7.
Then I would first have to select output 7 via midi command and then I could adjust the fader of input 5 via midi.
With the alternative method it goes like this:
assuming ADAT I/Os 9-16 are bridged
input 5 is mapped in TotalMix to ADAT Out 9
the signal appears automatically at ADAT In 9 because of the bridge
ADAT In 9 is mapped to output 7 in TotalMix
now the control can be done with a single midi command, which firmly controls the fader of output ADAT 9.
Since no more channels have to be selected, in this example it works for 8 channels at the same time.
By the way, with this scenario you can also create stacked fader groups and e.g. build effect sends (pre- or postfader).
Supposedly there is also a possibility in TotalMix to create the said bridge via software. But I have not succeeded so far (but this is completely irrelevant for the principle).
Maybe now it becomes clear why I like the Digiface USB with its 4 ADAT strips.