Try going immediately to your favorite Jack Vance books and seeing what kind of titles he used (Gene Wolfe is good for this, too). Vance usually used "translated" titles so they could be anything, usually a noun or adjective that related to the culture. I'm thinking of how in Alastor: Marune, the main character's people were all addressed directly as "Force." I think the actual title was "Kaiark" for a ruler. For Khromarium . . . "Scintillant"? "Entowered"? "Mantle"?

Chrisj, a couple of more thoughts: I would think the actual Hyperboreans in Khromarium would be very proud and jealous of their status, and I could see them working that into titles--something to remind the submen of their place. I could see this going in a couple of ways. Either you just have a system of ethnic markers in people's titles ("poloi Vikland," "poloi Ix," that sort of thing) or one summary descriptor that means "subman"--and this might even have become a point of pride for non-Hyperboreans who use it to signal that they or their ancestors carved out a place of power through force of will alone.

I also thought "Unhaunted" might be a good title for someone who has claimed and cleared a tower and supposedly gotten rid of whatever ghosts were lingering there.