ya but as you said you shouldnt believe everything he says. its like believing how he heard "xemnas talking with another person" down in that room. now obviously i think thats bullshit and just trying to interest zexion more into the topic because zexion didnt seem pleased when xigbar was talking to him about him so he had to catch his interest with something he rarely knows and that is a white lie by saying that. thats xigbar ya know.Xigbar indicated there may be a link between the two in his conversation with Zexion.
Now he may not be right, but he does eavesdrop alot and is bound to know thing concerning Xemnas and his search for this room.
i dont think the room of sleep is anything that deals with xehanorts memories. thats just me but i think hes just there to talk to his old friend knowing he has a connection on it but cant seem to wonder why and thus builds a room for the armor.Xemnas build the chamber of Repose under Ansem's castle. He must have unlocked some sort of memories within him about this room and likely it's location.
why wouldnt he just use castle oblivion to solve all his memories because he built those pods and experiemented with memories on them too?