Different firmware on surface and mixrack

We have 2 surfaces sharing a mixrack at the moment, but we have a larger production coming up, where we have rented an extra mixrack.
We are currently running 1.93 while the rented mixrack is running 1.94. Is this possible, or do we need to upgrade the surface connected to the rented mixrack?

Upgrade your desks and mixrack, there’s no reason to stay on 1.93

Good luck