if this is so, the ring should be either (althan) psionic or pure technology,
unless you opt for some sort of k'ta'viir techno-magery.
This is what I was thinking, also. How about this?:
The ring they are getting from Voriig Kye (I am assuming he required a service of them in order to do so - or he is getting rid of it because of the curse, someone is after it, or something like that, perhaps a combination) will not do what they want it to do. Sure, they can go the Tethoior route, but he will be unable to replicate the function, because he cannot replicate K'ta'viir technology. (No big deal sending them down a blind alley once in a while, not every plan or idea pans out.) But, what it does do is let them see what one looks like (as the ones made for the Jerak Ahrenreth were less capable copies, but visually the same). And, wouldn't you know it? Someone they know has one that looks just like that. Unfortunately, this person is not a friend and getting it from them will be an adventure in itself. Perhaps this person could connect to one, or more, of the PCs backstories.