Question: who was xemnas talking to?
Answer: I think KH 0.2 makes a bit more sense as to why Xemnas was talking to Aqua's armour in the Chamber of Repose. The armour is some kind of link to Aqua, and Xemnas used it to talk to Aqua in order to get the Ven's exact location in Castle Oblivion from Aqua, while being in Terra form in the Realm of Darkness.