Hi CTrice,
From what I’ve read about Eurorack (sparse on experience ATM, take this with a grain of salt) you’d use a passive connection between multiple bus boards within a single case, or with two separate cases you’d use a special module in both units to avoid signal loss.
At least that’s what this Doepfer technical page has to say. It’s for their A100, and this post mentioned the A100PSU3 as viable – so I think we’re on the right track. Whether or not the same Doepfer modules will work equally well for video and audio sync signals is something I’m uncertain about. We can always hope passive alone will be good enough too – but it looks like you do have options. 
Someone else will give you an immediate and direct answer in like 2 seconds, but hopefully this leads you in the right direction until then.
And if you’re using the LZX Vessel:
- Two 3.5mm TRS jacks on the right diagonal face allow distribution of the EuroRack power rail’s CV/Gate buses from case to case using readily available stereo 3.5mm cables.
Screenshot below of the relevant section from the Doepfer link above.
