My 7 yo is in this phase right now, too. He was crying and screaming at the xbox yesterday because one of the menu options wasn't working the way he wanted it to. In the moment of his distress, I explained he wasn't in trouble but that he needed to turn off the xbox, go calm down in his room, then play something else for a while. Screaming at the tv won't fix the problem...it's just a game...it's not worth getting so upset over it.
At first, he didn't want to hear my instructions, but I stayed with him until he followed through. At times with my kids, it's been necessary for me to step in and turn it off for them to make sure they follow through with my instructions, but this time he did it on his own. He went to his room, I heard him rumbling around in there for a while, then he went and played with other toys for a while. Later that afternoon, he asked if he could have the xbox back. That was the teachable moment--I explained I hadn't grounded him from it, that he wasn't in trouble. I told him that one of the things he needs to learn is how to handle his own frustration. And when he's not handling his frustrations himself, that's when I have to step in and make sure it doesn't get so out of hand. But if he can monitor his own emotions, then I won't have to do it for him. If he knows when it's time to walk away from the xbox for a few minutes so he doesn't get so upset, then I don't have to come in and make him turn it off.
So I told him it was his decision on whether to try it again that day--that I trusted him to make a good decision and to handle his own emotions. As long as he doesn't let it get the best of him, he can make his own choices. Once I hear him losing control of himself, I'm there to make sure he walks away until he's back in control of himself.
His actions have consequences. Not controlling himself means that someone else has to intervene. But if he controls his own manifestation of his emotions, then he has more freedom of choice.
At the same time, his emotions aren't bad or "evil". It's legitimate to feel frustrated or sad or angry sometimes. But the emotions are there as a cue for what is needed (change of activity, exercise in patience, comfort from someone, whatever), not as an all-powerful force that must control your behavior and experience of life.
Emotions are like indicators on a dashboard, not the steering wheel that directs the car. Use emotions as helpful input and feedback, but the decision-making still happens at a whole different level.