Nellie, just my thoughts/what worked for us.
I haven't read the whole explosive child book, but I've read bits of it on threads/the free introductory bit you get on amazon, and although I feel that it does apply to DS when he's in a heightened state of stress, I don't know that actually it does apply all the time. Yes he has trouble accepting not being the best/the winner, but isn't that an age thing? And he really has no idea when to back down and stop but again I think it's a combination of age and personality. I remember as a teenager always wanting to have the last word and my mum got really frustrated with it. What I did find useful about the explosive child theory is the affirmation that yes some children get more wound up when you try to deal with things in a punitive way.
The thing that I have found is most important is not to get drawn into a battle, which might be what they mean by not withdrawing treats etc - I can see (and this is definitely the case with DS) that it's easy to get into a cycle where you say "That's it, no sweets at the cinema!" and then they continue to misbehave so it becomes no cinema, no TV at home either, losing some other toy, and in their room for some ridiculous long time, and they've been shouted at too, all over some minor thing. It's not helpful. I remember a memorable afternoon with DS where I ended up threatening to take some sweets off him, and his train set, no TV and he had to stay in his room until dinner time(! 
) and also roar-screamed to the point of going squeaky on that walk home. I think I might have pushed him away from me and caused him to fall over too :( It still wasn't stopping him from winding me up and laughing (even after he got up from being upset!) and I gave up and cried most of the way home while trying to fight the urge to drag him home by the ear. Then when I got back I had to follow through on everything I'd threatened which just made me feel awful because it was so ridiculous (although I did then have his sweets 
)
Like you I had found that time out in bedroom was working OK in our old house, but it wasn't working here. In fact, it often ended up as either me or DH trying to hold the door shut while DS would make a huge game out of opening and closing the door and laughing, or DH would basically go in and hold the door closed from inside or actually I have no idea - possibly he was restraining DS somehow, whatever it was it made DS incandescent with rage/hysteria and used to really upset me, even though I had no better way of dealing with it. It would drag out for ages and DS would be so upset and sometimes he had nightmares :( so horrendous but neither of us had any idea what we were doing. Of course by the end DS probably had no idea what had started the whole thing either.
We had to take the fight out of it. So what I did in the end was sat DS down one time when he was calm and said, look, this isn't working and we don't want to carry on like this. He was all helpful and earnest about saying that he wouldn't get cross - I said, it's OK to be cross, it's not OK to hurt people and push/throw things. Again he promised that he would not do that any more, but I know that in the moment, he won't be able to remember that. So we talked about some things he could do. For a while we'd had a "calm down corner" which was supposed to be a safe/cosy space but we have a small room and when we moved furniture for more space, we didn't have room for it. So although he said he wanted the calm down corner back, he decided that it would be OK to calm down in his room. This DID help because some of the time even when hysterical he was able to respond to being reminded that he helped decide this. I also told him that any incidents of hitting, rudeness or pushing/throwing things, would result in a 30 minute screen ban. Now, I can see that this is contrary to the explosive child advice (although it's not removing a treat/reward but a more everyday high value thing for us) and it might not work for all children, but we are careful with it (OK, I am careful with it - DH is likely to keep doling out increased times which winds him up) but the important thing is to state the sanction. "You hit mummy, you are banned from screens for half an hour." and then deal with the emotional fall out rather than trying to regain control by slamming him with more and more punishments. It's a clear consequence, it's not too severe - some would say not severe enough, but I actually think that's the key really, if you think about it, the emotional volcano thing is all about "Argh I can't get my own way. NOW I'm going to get this horrible punishment, it's not fair! Why won't they listen to me?!" and they explode beyond all reason. With this it's almost token it's so mild (I finally understand what people mean when they say they use a tap on the hand that doesn't hurt but makes a point! I'm not going to start doing this, but I never "got it" before and now I sort of do.) But it's still enough to be a bit of a deterrent, because it parts him from his beloved Minecraft and Stampy. We don't have to fight to enforce it - even if DS says "Haha I can watch TV anyway" we can pull the plug or remove the batteries from the remote control, he doesn't know where the actual buttons on the TV are and can't figure out the plug thing yet unless he sees it done. We don't restrict TV time really apart from this so it's not like he's losing precious minutes from a short time period (although that can work too).
We do still take him to his room, if he is unable to calm down or he is continuing to hit/punch etc, and (this is the only part I feel slightly wrong/guilty about) we now get him to stay in there by saying that his sweets, which he buys with his good-behaviour reward money, will go in the bin. I feel bad because it's the threat of losing a reward, but it's literally the only thing we use it for (DH once used it for something else and I went mad at him, now he doesn't!) and again, we just needed something to take the physical fight out of it. It works, possibly because he's calmer by the time he's taken in there anyway. Sometimes he even goes by himself when asked!! 
When he's calm then sometimes we have a little talk and sometimes he just comes out or we say he can come out and he says "I'm OK, I'm playing in here now", which is also great.
Also, these issues - violence and rudeness/aggression in general are the only things that we use this for. Other issues, cleaning up, getting places on time, eating, tooth brushing, general behaviour, road safety etc, I try to manage more in either a direct boundaries/related consequences way, a positive way, using play/humour, reasoning, closed choice, pick battles, generally encourage him rather than stand over making him do it, etc. And we still give him "stars" for good/helpful behaviour. It's (for me) a case of isolating the issue, having a set formula to deal with it, and then it's easier to deploy that formula without getting emotionally dragged in which was what was happening before.
But there has definitely been an improvement with time. I think we'd been here 6 months and one day he was angry with me for pulling him out of a room where DH was sleeping and he came and roared at me from a distance, threw a soft knitted hat at me, and un-tidied my shoes declaring "Now I've messed up your shoes and you'll have to put them back all by yourself!" before slamming his bedroom door, preteen strop style! I was just really astounded. He'd handled himself so much better and I suddenly realised that we hadn't had any serious incidents in ages. He used to get screen bans about once or more a day but now he's unlucky if he gets one a week. Funnily it's coincided with him starting to put words together into sentences in German so I wonder if he feels more able to communicate and hence less stressed. I also noticed that he was more explosive, aggressive and argumentative on days when something bad had happened at kindergarten but he didn't always tell me straight away. So things like one of the other kids had hurt him somehow or something frightened him. I used to do a little debrief at the end of the day with him which I haven't done for ages which I should bring back. It's just about talking about feelings - I think that between about 4 and 7 must be the hardest age for a big move. They're old enough to realise intelligently what they've lost, to have an attachment to a place, to remember and hence miss it, but they're not emotionally mature enough to recognise that the new place will be just as good once they get used to it and there are lots of exciting things about going somewhere new. And newness for anyone is overwhelming, to deal with that without having a familiar, safe, known base to go to is hard. I know when we first moved here DS said most often that he missed his bed and his bedroom. We've tried to make his bedroom a special place and given him a say in how it's decorated, furniture, pictures, curtains, bedding etc. He loves to move his room around and I think it's helped him to make it his own space. If there are family members he is close to you could ask if he wants pictures of them, either on his walls or in a book or something? Do you have a long term plan that you can explain to him, and if you know when you're likely to visit home, then that can be reassuring too.
Sorry for the epic post and semi life story! Apologies I haven't replied to anyone else. I'll come back later!