There are several ways to handle this. If you have a matching set of Waves, Dante, or Madi cards in both consoles, then you can definitely send audio back and forth between the different systems using those cards. However both systems need the card.
You can also send the audio over the A&H proprietary connections. To do this you’ll need a Gigaace card in one of the systems, and a free built in SLink port in the other. If you are using the built in port for something else, then you’ll need a free Gigaace card in each system.
Hopefully that helps.