Dylan used to wake through the night too. At one point, we had considered having him tested for Sleep Apnea, because he was waking so much.
Have you tried Melatonin? I know nothing about it, have never used it, but I know alot of people here have used it with great success.
FWIW - the Seroquel really didn't do anything for Dylan sleep wise. Made him a little groggy, but didn't hold out for him through the night. Now he's on Abilify, and it's GOOD NIGHT DYLAN, straight through. Not saying that it would work on your difficult child, but just a thought.
Janna