I went back and reread both... there are many things that can't be ported easily to Cairn. The compendium classes would have to go. Everything that requires a "discern reality", or a +INT (or +WIS for perception) roll is hard to translate because Cairn doesn't have an intelligence stat or perception mechanism - it relies on player intelligence and description of their actions.
That's a bit of a problem with Cairn: with so little rules, most of the supplements can only give advice instead of hooking into the system.