For several years I use a redundant Cantabile/Computer system with two independent computers (all mounted in a box; 17 kg).
I use DIN MIDI and MIDI merger(s) (reliable; hot plug capabable).
The two systems are always synced regarding songs/states.
I can switch songs/song states/show notes (and other things) via a cherry numpad or from the touch screen of the 2in1 Convertibles.
If I deeded a second masterkeyboard I’d first try to use MIDI Thru from the main masterkeyboard or use another MIDI merger.
For some time I also have my personal monitors (KRK GoAux4) directly mounted at the box (now it is about 22 klg)