I was going to suggest that you need a sleep study since this is not insomnia (and this is an insomnia forum). Since you had a sleep study, it is up to your sleep doctor to interpret your results and provide treatment options. It sounds like you also have a delayed phase disorder since you can't fall asleep until 6am, which means your body temperature rhythm is shifted too late. This often requires chronotherapy (going to bed 3 hours later each day for a week to shift around the clock) so ask your sleep doctor about this as well.
Dr. Jacobs