I hate to start with this, but im phone typing so have to be somewhat brief- I think your psychologist is on the wrong track. if he's motivated to do well, and still failing, I think he's unable to meet the goals for some reason. I think the transition is likely the problem, and thats not uncommon. Is he verbal enough to tell you how he would like things to go (during a calm time)?
Here are a few other ideas:
Have you tried going in instead of DH?
What if you brought in a drink?
Played music?
3 minute warning that transition is coming?
Story before getting up
Picture schedule in his room
Reintroduce card system
Good morning song
Has your it taught you anything that might help? Deep pressure, brushing, joint compressions, etc?
I'd even do tv if that helps him stay calm.
I've seen some moms here mention having their kids sleep in their clothes so they can skip that step, then doing breakfast in the car. I'd pretty much do anything that worked. You could always change it back to something more ideal down the toad when things fall into place a bit more.
I agree that breaking that battle cycle is key, which is why I think the psych's advice is off base. I've said before that your Ds reminds me of mine , and I can tell you that the more we try to crack down on things, the worse things get. The more i can show im on ds's side, the better thongs go. I think I may have mentioned The Explosive Child up thread. There's also a website with videos that are helpful. I really think it would be a good match for you guys.