I haven't tried it but if you connect both laptops using ethernet to a network switch or a router. Enable OSC output on your Mac and then enable OSC input on your PC, I dunno if that works or not. You can also get the rtpMIDI driver here: https://www.tobias-erichsen.de/software/rtpmidi.html and then have both laptops receive midi from your midi controller that you're using to control Arena.
I preffer to have the same composition loaded in the two machines and a switcher, but just use one. If a crash happen, switch to the second laptop wich is allready throwing some main content, and move your controller, etc.
I try'ed using two laptops with same composition linked through osc , and used a controller to trigger different contento on two laptops using rtpmidi. But if you ask me, using that configuration just for backup is a waste of resources.
And for synchronized stuff, is easier to throw an audio signal to 2 laptops and sync with stmpe, than send osc messages all the time for just in case of..
What about for having Ableton on a Mac send OSC via the max for live devices, over to Resolume on a PC? Can this be achieved with just using an ethernet cable to connect the two directly? Or any adapters, software needed?
I do that all the time running Qlab or Vezer on a Mac to control Resolume on a PC and it works great. You can use a direct Ethernet connection between two computers or use a hub or a managed/unmanaged switch.
Two things to keep in mind:
1) If you use a direct Ethernet connection, just make sure your two computers have Auto-Medium Dependent Interface Crossover (Auto-MDIX) and if either doesn't then use a crossover Ethernet cable (twisted pair).
2) In most cases, it's probably best to set your IP, subnet, and gateway (assuming you have gateway) manually rather than to use DHCP. If you prefer DHCP, I would use DHCP reservation and set specific addresses on your DHCP server using the MAC addresses of your devices.