First of all, there’s a new application example in the manual on page 16 to show how to link two ZMACS units such that all connected amps ultimately route through the attenuator loop and cabs on the second unit.
https://fryette.com/content/ZMACS_Owners_Manual.pdf
Of course, you can connect cabs to the first unit, but they will only receive signals from the heads on that unit and no attenuator.
As far as controlling them independently, you don’t really need to. Just program your midi presets simultaneously for both.
In other words, select a midi preset, then set and store the settings for the first unit, Then set the second unit the way you want it to coincide with the way the first one is set and hit store on that unit. Each unit stores its own presets.
That’s what we do with the two units set up in our demo room.
There are circumstances where you will want to mute any selected amp on the first unit when playing an amp on the second, but you can also store that mute function as described above.
Hope you find this useful.
Dave