How do you know when you've done all you can?

My husband and I finalized on an adoption in 9.25.08 and although we'd seen off the wall behavior with my son (5 @ placement, 7 now) it had all gradually stopped months before we finalized. There was never a question that he'd witnessed and endured a lot of abuse while in FOSTER care. Just recently it's escalated to pooping out of anger, hitting me, making threats about "Rape" towards his sister (age 10) and myself. He's told me that he only behaved so I wouldn't send him back. My son is in therapy and awaiting a psych consult. He has ODD, ADHD, tested positive for an extra Y chromosome and a genetic syndrome. He has a history of sexual behavior (touching others) and is very dominant... I'd even say that he enjoys demeaning women. He has told us that he doesn't love us, has made false accusations about being abused in our home, makes sexual comments about everyone. We've tried everyhing from time-outs, revoking privileges, taking toys, even cancelling our summer vacation. My husband and I must be with him at all times, and he has a "Shadow" at school because of his behavior. He is currently in the behavior unit at school for stabbing a boy, knocking down a girl and banging her head on the floor, etc. Someone please give me ideas on what to do. I desperately wish to help my son but I'm clueless on what else to try. My hubby and I are both drained beyond belief.