You were correct, it was easy to open up the new locations through the catacombs, so I pillaged Atrixus and found demonologists in the Demonologist hut which you can access through the flying platform in the main yellow picture-circle (or whatever that is). Now things are going much more smoothly.
I will, however, eat my shorts if KBDS has the early KBAP bug where disbanding troops count as losses
