I'm not sure if you're not mentioning spanking because it's not politically correct, or because you haven't used it. If you have used it consistently to no avail ignore this, but time outs rarely work on difficult kids.
Constant removal of things is much more cruel than a split second of discomfort for kids, because they are constantly being deprived of positive activities, not benefiting from the positive interactions with loved ones and friends while being kept home, and losing things they care about. I get it that the point of discipline is to be unpleasant enough to deter the behavior at a warning the next time-but if it isn't, then it's not effective.
Kids, especially with ADHD , don't really care about a warning that they wont' go to a fun activity, because it's sort of abstract, it's in the future, and it's no real skin off their nose, because they'll be pretty comfortable at home anyway. Your son hit you, and pushed you, and you sat him on his bed. Yes, it got long and arduous, but really, sitting on a bed, is not so bad.
And if he gets mad and throws a fit about losing the privilege or item, then what's the discipline for that? And talking back? You need something quick, firm and effective that does not end up leaving him home, resentful and bored because he isn't doing things that could enrich him.
Check out his book, it's really effective and great for boys this age: Back to Basics Discipline by Janet Campbell Matson. You don't need to get angry, but you do need to be firm, consistent and concise. You're right, DON'T PREACH AND BE A BROKEN RECORD. Calm brief waring, and the outcome is up to him. He's gotta think fast and care about the outcome.