How can i emulate a monitor/switcher controller in ableton using my interface's two outputs?

[OcelotDelta]

I have a Motu M4. It has two outputs. 1/2 and 3/4. The main volume knob in the front controls 1/2, i found in ableton i can switch the master to 3/4 instead of 1/2 to output master audio to my second pair of studio monitors. but my interface outputs 3/4 channels at full volume. even with my monitors set to lowest volume on the back its still too loud.
is there some way to do the following TWO things?
1. make some sort of macro or hotkey/shortcut/bind that will switch master from 1/2 to 3/4 without my clicking the options?
2. make some sort of bus that i can toggle on and off that will let me switch outputs? like a bus that is routed to 3/4 that i can switch to away from the normal master that outputs to 1/2? and then have seperate volume control for this bus that outputs to 3/4? i guess this is all one big question though.