Is this attachment related?

My son, 6.5 (adopted at 5.5), has a variety of special needs which may or may not be accurately diagnosed. He was pretty significantly neglected (orphanage) prior to adoption, and we expected attachment issues. The problem is...we didn't see issues that were exclusively attachment related since his diagnoses (autism, global delays, possible exposure, ADHD) all have similar symptoms. At first, he raged/was destructive/self-harmed/showed no acknowledgement that he was aware of us being any different than a stranger at the store (by at first, I mean the first 3 months or so). He didn't reject us and appeared to like us well enough, he just didn't show a preference. He doesn't seek out affection from other people, but he doesn't seek out affection from us often either. Now: He does make good eye contact, he will sit next to us or on our laps if engaged in another activity (t.v., book, etc). When going to sleep, he wants one of us to lay down and cuddle with him and is upset when we leave, but I think he would react the same way to anyone. He is actually better behaved for us than anyone else and seems genuinely proud of himself when praised. He is happy to see us when we return but does not seem to miss us when we leave. He does allow himself to be comforted if he is hurt but does not seek it out. He also: has behaviors that he reserves just for us that he knows will push buttons. Continues to have pretty significant rages/melt-downs that include destruction and violence (pulling hair, pinching, scratching). These actually were almost completely eliminated for a couple of months and then increased SIGNIFICANTLY with no known cause. He is typically less violent with us because he knows we are willing to restrain him, but recently he has acted like he is seeking out the restraint. Has started crying after rages (sad crying, not angry crying) so that you think he is finished. He will say all done and relax his body and then turn around and attack you. He has an incredibly believable fake cry but then will turn around and laugh in your face if you call him on it (this one is reserved for us and very disturbing to see). We are torn on how to react to him, because we don't know the root of the problem. If it is just behavior due the combination of his diagnoses and getting his own way for 5.5 yrs, we would continue with the status quo of high structure, high expectations, very firm parenting. He seems like he is able to relax if he knows that we are not going to budge on the rules; if we react to little things in the way you would react to a typical child (redirection, joking, etc), he will escalate 100% of the time to find the boundaries. But...If it's attachment related, I wonder if we're not shooting ourselves in the foot by being the super strict authority figures when everyone else is "fun." Part of me feels like his attachment has been pretty typical up to this point. He had no real paradigm for family/attachment so it makes sense it would take time to develop. Now that we're nearing the 1 year mark (and seeing his cognitive ability increase significantly), it seems like we're seeing more behaviors that look like attachment issues.