8 year old son's temper and emotions - what to do?

I have 4 kids and one due very soon.  Oldest is a girl, 10 followed by my 8 year old son, a 6 year old son and a 3 year old son.  We have another boy due the later part of September.  

My 8 year old son has had a huge issue with controlling his emotions since he was little.  When he was 2 he would throw himself to the ground and bang his head against the hardwood floor to the point where we would have to put a pillow underneath him or hold him so he wouldn't hurt himself.  As he got older if we had him take a time out in his room, he would kick and punch the door.  And even now, if he gets really angry, he'll hit, kick, throw things at the ground, slam doors, hit the wall, etc.

My son has a very sweet side to him as well, although he can also get very self-centered and focused more on himself than others.  But he is VERY emotional.  He can have his feelings hurt very easily.  If we ask our kids a question and he has the answer, but we call on someone else, he breaks down in tears or yells "I WAS GOING TO SAY THAT" (which some of the time you KNOW there's no way he was going to say it because it was actually a question more for the 10 year old).  

We have tried SOOO hard to help curb his behavior and help him not get so upset - to help him be more aware of his feelings.  You could be talking to him about something he did in the nicest tone or just giving him some friendly advice and he'll get SO defensive.  

When he was 6-7 we did a reward system where the kids earned pretend dollars to buy stuff at the family store (candy, game time coupons, toys bought at the dollar store, etc).  It went real well for a while until he started stealing the dollars (he has an obsession with money he's had for a long time).  We worked with him through 3 incidents and finally had to do away with it because he couldn't stop stealing.

Recently when he started being real destructive towards stuff in his room for about the 3rd time in a month, we took away everything in his room except a dresser and his bed.  He had to earn back his stuff and priveleges with points he would earn from doing his jobs, homework, etc.  If he could go the whole day without losing his temper, he would get something extra given back for free (in addition to him using his points).  If he had a major fit (kicking, throwing, etc) he'd get something taken away again.  

This went VERY well for a while.  The point was for him to be reminded of how his things he has are a privelege and how his temper is preventing him from those priveleges that he has in his life.  This worked pretty much until he got all his stuff back, which took about 1-2 months (with only a few tempers and fits) but now he's right back to the quickly lost temper.  

If he has his mind set on something, like about to go play in his room and we ask him to, say, go brush his teeth - he will get upset.  It's little things like that which are such a big deal to him, but to any other kid is no biggie, that he'll totally lose it.  

Anyway, sorry for all the info but I feel like it's necessary to know a lot of this and the examples in order to truly be able to provide any advice.  I've posted on forums before about this when he was younger and just can't seem to get him to handle his temper.  I worry that if we can't get this taken care of now he will have an even harder time with it when he's older.  

What can we do?  I've thought about having him see a child psychiatrist or psychologist but my wife is very opposed to that.  Although she's at the point where she doesn't know what else to do either.  

Oh, one last thing that I think someone might ask us - I work out of the home 2 days of the week and in the office the other 3.  My wife works from home as well which she's done for the last 5 years, but she does it while the kids are in school or after they're in bed (she has a lot of leway with her hours).  Otherwise she's a full-time mom taking care of the clan, so it's not like she's been out of the home.  

Anyway, any advice would be very grateful.