Kane will be defeated by something that is in some way, not living.
In the Armada puppet show, Avery said that Kane is stronger, faster, and smarter than any living being. He put a suspicious amount of emphasis on "Living." That seems like forshadowing.- Jossed as far as we know. We defeat Kane as we would any other opponent without any in-story supernatural buff or whatnot. However, the cinematic that plays afterwards shows Kane's head empty, possibly implying that he lacked the brain from El Dorado (though it could also imply that it was destroyed/teleported by the Machine at that moment) so he might not have been operating at maximum efficiency.
There's an in-universe explanation for how player characters can chat in the skyways across huge distances.
They use pirate radio.