With DKs, Kael is a piece of cake. Of course, you can't pick up and use the staff for CC immunity, so that will make it more interesting. But popping your armies right before Kael comes out in phase four should make the toughest part of the fight (mind control) a non-issue.
You should try Malagos as well. I do it four times a week with teams of ten each and he's at 0 hit points by the end of phase 1. You won't be able to do that with only 5 guys, but should be able to get rid of most of his hit points. Phase 2 is a joke, and if you spread your mounts out, target Malygos with all yours toons, then hit 1,1,2,1,1,2,1,1,2 with everyone in phase 3, he should be down before you are.
