FYI: I love that part of the country. A group of us makes a trip down there every year to ride (motorcycles) through the mountains. I'm jealous!
I am in the same predicament with basement heat. I have 3 vents coming off the main-floor heating ducts wide open to the basement, and it is still easily 10 degrees cooler than the main floor. So, that may not work for you either. I am considering other sources of heat down there...and baseboard is the current frontrunner.