On a trivial note, you CAN make adjustments to the MIDI configuration of the MM in its CONTROL>MIDI CHANLS menu, and the 8 Global slots allow you to have a different configuration for each typical set-up of your gear.

My set-up is not dissimilar to yours in its complexity. I generally find it conceptually and practically easiest to have each Elektron machine sequence its own sounds, with the only external MIDI received being Tempo and Program Change from the OT or from another sequencer altogether.

To maximise flexibility, you might consider putting the MM and MD on the other side of the Unitor8 from the OT - just consider them as other synths to be controlled most of the time but also used as sequencers for special purposes. So one possibility would be KBD Out to OT In, OT Out to Unitor In, OT Thru to another Unitor In, and than Ins and Outs from all the other gear to the Unitor.

I think that a better option would be KBD Out to a Unitor In, then each other unit connected with In and Out to a port on the Unitor.
I believe that the Unitor8 has 32 different configurations that you could switch between to select a different set-up. Obviously, you would need to keep note of which global settings were required for each Elektron and other synth to match the Unitor configuration.

How many other MIDI instruments do you have?