Bernarada
I think what you're after is "sub mixes" or a "master volume" where each track maintains it's own level relative to each other, then there is another fader that can bring that entire mix up or down. Groups unfortunately don't do that, they could cause ever track's output level to snap to the level of the group control, losing whatever balance you had previously set up between them. Example: a knob that controls track 1 setting level to 32 and a knob that controls track 2 setting level to 80. Then a knob bound to a group with both tracks 1 and 2. As soon as you touch that group knob, tracks 1 and 2 get the output level of that knob and the values from the first two knobs are lost.
Your best bet right now is to do that in the host, let Mobius track levels be your submix, then route all of that into a gain control in the host that you can move up and down.
A more complicated option is a "control script". What that does is get called every time a CC knob moves, and you can then use that value for any purpose, such as making relative adjustments to track levels without forcing them to any specific value. It's kind of hard to set up, and it's been awhile since I've looked at them.
Improvements to track mixing is definitely something on the radar.