He needs to be in Military school NOW! I put that at the top because it is the most important thing here.
After reading this thread, I thought I'd add something that perhaps hasn't been considered. It's from my experience on the other side of this equation as the brother of a boy(s) like this, and someone somewhat like him myself at one point, but without the lack of conscience he seems to have or fear of consequences (that part might make him a truly dangerous person in the future). And from my experience with MANY of the grown up versions of these kids, once adults.
He needs to go to military school or another similar place NOW!! Too bad if mom feels bad, she should have been correcting this earlier. If he had a vision problem, dyslexia or other, she would have been. But behavior reflects personally on parents, so they wait and try to fix it themselves. But it sounds like hes got a problem with the "wiring".
Yes, he's 9. And every day he loses being the same as he is now, is another day his neural networks are solidifying him into this person you can't stand and who's not fit for society.
Do some studying about character formation and kids and you'll see that these patterns are set from a VERY early age. You are on the cusp of it being too late to "change" him. He needs that structure NOW.
Yes, people can change, but they have to want it. This requires SELF-AWARENESS that a problem exists, and your son just doesn't have it. (You mentioned that he doesn't get the "why" of rules) He needs to go somewhere to get it. And no more PS3 EVER. Studies on video games show increased eye hand and reaction time, but no development of social skills. Look for studies by Dr. Prof. Ryuta Kawashima, Tohoku University.
Take what you hear from psychologists with a grain of salt; their belief in "changing" people comes to a large degree, from a very optimistic view of humanity. It must, or their work would be a waste. By the time he's a teen and his hormones get running among some disconnected wiring, he's gonna be a menace (fully formed gratification/reward centers in the brain, but unformed connection between immediate action and consequences= zero impulse control). For the reality version, talk to anyone working in juvenile detention about "changing" kids.
Subtle solutions wont cut it now. Punishments, talking to him. He just doesn't get it. He'll only learn that he can withstand punishment, not connecting it to what he's done. A militaty school lets him see his actions in a group setting that depends on his actions, and suffers the consequences together. It's a microcosm of society, where his authority figures AND mates will bring social sanction against him, providing a complete picture. If he can't make the connection there, he never will.
He doesnt like sports? Sports saved me, but everyone's different. Get him into art. Make HIM create, not just react. This saved my brother and in adulthood too. He found his place in landscape architecture and he's truly on another level artistically. All that ever seemed to be wrong with him, that level of dysfunction comes out as the opposite now, in his work. But it came after a long sexual addiction that almost cost him everything and lost him 2 businesses.
This brother and my cousin that basically grew up together while my Dad was at work. They were a holy terror together and apart. My cousin never got the help he needed and did a dime and half in San Quentin. My mom saved my brother, and liberal beatings from my Dad. It was like a daily routine, Dad comes home, beats brother, have dinner
But you could see he just didn't get it. And he was never as bad as your son.
In my former work, after many years of trying to find out the difference "good" people from " bad". Bottom line, only one thing separating those in prison with those outside of it. Impulse control. That's all. They're all or mostly sorry, or wish they could take it back. They aren't evil. Just lack impulse control.
"Good" people think the same thoughts, as you know. Take what's not yours, employ violence, do what you want. We all think it, at least for a flash. But those "bad" people do it. That's the difference.
Point is, it needs to be dealt with now if any hope of changing him exists.
Good luck, Brother. You are a saint for trying.