That's pretty much what I'd been doing, overall. But I also want a specific sort of tone and connotation. Either something about war, or power, or loss, or ancientness, or trade (not as much anymore, it seems too weak and a bit too traditional-4X), etc. My requirements for the "right" name are many and subtle, and I have not been able to really articulate all of them even to myself. That's part of what I'm doing, is figuring out what works and what does not.
I don't see the Zenith themselves playing an overhuge role in the expansion, honestly. Interaction with them is likely to be fairly mechanical, except if they join forces with the player or the AI. It's not going to be sweeping diplomacy trees or anything, more like just shops in other games. This is a military game overall, and the diplomatic options added here are not intended to be overly advanced. It's meant to add/enhance military options, nothing more.
So the real thing being emphasized, then, is not so much the Zenith themselves, but rather their stuff. Their toys, weapons, the stuff we buy from them and find lying around. That's the underlying theme of this expansion, although there will be unrelated divergences for variety and gameplay reasons. A lot of players will get excited about having a third nonhuman faction, and that's cool too, but I think it is not quite the focal point.
I'm actually pretty happy with The Zenith Remnant or Zenith Remnant, that's pretty much heading into home plate for me at this stage...
Anyway, that's it for me tonight!