Yeah, the guy they need to get out of there (and replace with a legit, defensive-minded seven footer) is Bass. Sully and KO need playing time, and you can probably get by with them playing together for 15 or 20 minutes a night... but you need an Asik-type to shore up the middle defensively.
Long-term, I'm not sure there's room for both guys, if they both develop as we hope. I really don't want to see either guy at the 5 spot for more than those limited minutes. For now, though, I think you've got to hold onto them and keep developing them, because I'm not sure how much trade value they really have. I like Sully, but I don't see him as being good enough to be the centerpiece for getting Love, as an example. And KO was looking better at the end of the season, but I don't see how he's got a lot more value today than he did on the day he was drafted. If those guys can keep playing and keep developing, they should have a lot more value as trade assets in another year.