I would suggest that if your insurance pays for the second study that you have the second study done to be using accurate seting on your C-pap. My settings begin at 4 and slowly ramp up to 8. I do remember the therapist who came telling me that the machne I have was rated for a max of 10. If you really need more than 10 because as you describe yourself as a "large" man, This machine is not helping you and you are not getting the relief from you headaches. I used to have migraines too, not sleep at night, and be sleepy all day. I even feel asleep with a drink in my hand and it dumped on me and woke me up. Also when I saw my pulmonologist after my first using my C-pap they were very pleased with me being able to sleep for a period of 5-6 hours at a time.
Hope this helps you. Feel free to contact me,
Linda