I expanded a PreSonus 1824c interface with a Studio 192 interface via ADAT optical to get some extra inputs. The 192 provides the ADAT clock out, and the 1824c syncs to it. However, both interfaces also have word clock connections. It seems to me that it would redundant to hook those up as well - sync is sync, right?
Right - sync is sync, but there must be only one master and everything syncs to that. So if you're setting up the the 1824c so that it syncs to the ADAT input, then you shouldn't connect the word clocks together.
However, because ADAT optical sync is more prone to jitter than word clock [internal reflections vs. standing waves], it's possible that using the word clock setup might sound better. And to further enhance your listening enjoyment, you can try to decide which word clock sounds best when used at the master.
Or you could just accept that modern day converters do such a great job of filtering jitter that it's not worth fussing about. But it never hurts to be curious.