Not a dumb question as it can be confusing to understand the various sync options in the system when first encountering it. And the answer applies to any eurorack case utilizing the Doepfer power bus standard (basically every case I’ve ever encountered), not just the Vessel case.
My understanding is that there are two different versions of Prismatic Ray as far as sync is concerned, though I’m unsure if the 2nd version is out in the wild yet. The manual and reference cards don’t include details about the 2nd version.
Originally PR worked with the power bus to pass sync information meaning that the PR can be located anywhere in a case as long as it is connected to THE SAME power bus as whichever module is generating sync (like Visual Cortex for instance).
I’ve heard that the newer PRs have RCA connectors on the back to connect to other modules with RCA sync connectors on the back. The RCA connected modules daisy chain their sync by plugging one into the other so your only limit is needing to place modules within reach of whatever length of RCA cable you have to span between them.
What I’m unclear on in regards to the updated PR is whether or not it can do both types of sync. Can it still sync via the power bus sync if so desired?
Last point regarding a unique wrinkle the Vessel cases bring to the party for these sync options … the RCA & 1/8 inch bulkhead connectors on the inside and external side of the cases allow you to connect both the power sync bus and the RCA sync bus from the backplane (inside the case) of one case to the other via the external connectors … practically this means you could have whatever sync generating module you like in one Vessel, and as many PRs as you like spread into as many Vessels as you like, all connected with external cabling on the Vessel bulkhead connectors. This, for me, is the most useful feature of the Vessel design.