I'll just add that the above info is good, you'll also want to make sure both decks are using 512K boards with the same coder version. You CAN run it with mismatched sets, i've done it numerous times, but you will run into issues.
One thing these setups cant handle is if you are scanning two very busy sets on each one where the audio and display is updating a lot. The CPU in the master radio can't keep up and after a while you will get a HW ERR and reboot. If you select a Network Mode other than Summed audio and Alternate display this isn't as much of a problem.
FWIW, pairing an M7100 with its faster CPU and an Orion can alleviate that problem but usually generates a new set of 'quirks'.