My DS was/is a fairly intense guy. We found "The Explosive Child" to be a fantastic resource for us. The name is a bit much but it really, really helped us.
The other thing that worked in our case was to give DS as much control as possible over his day/life. Now of course at age 6 this is a bit of a challenge but start with little things. We shifted from saying demands like "get ready for bed" to "what do you want to do first, get jammies on or brush your teeth?" when we could. Both have the same end result but in the second case, he got some control and he wasn't constantly escalating every little thing into a battle and we had more energy/patience for the battles that remained. We also found that he was a bit more cooperative on the occasions that we did just demand (either because we forgot or because it just wasn't practical).
Anyway, not sure if that will help with your guy but I feel for you. My DS is now 11 and I can still remember him around that age and the absolute fits that he threw. He can still have his moments but nothing like it used to be.
