is there any proven connection with the oblivion towers/sigil stones?
I'm not sure of any definite proof, but it has been speculated several times that Dagon's towers play some role in getting through the liminal barrier. Especially seeing as how removing their stones shuts them down, thus closing the Oblivion gate. Though beyond the fact that they both influence the barrier, one holding it and the other tearing it, I don't see any other links. Though I would guess those towers were the echo of the zero tower as well, Dagon and his daedra building them in the same way the elves did, but they constructed them in a way that did the opposite of the Nirn Towers.
It reminds me of Numidium being said to have "dis-creation", though I suppose that only applies to its ability to stomp on things and conquer provinces.
EDIT: Oh, and if you haven't tried already, you can search for more threads on this here, or go on over to the Library and look up the Guardian theory. It explains quite a bit, though the theory itself is not accepted by everyone.