I'm thinking it's more of a signal
quality issue at this point. The VHF section of the Channel Master antenna is just not that good when it comes to rejecting multipath. The
specs indicate a rather wide VHF beam width which is not good unless a clean, reflection free signal is seen at the antenna. There is no reason why you shouldn't be getting the desired VHF channels with one set connected directly to a proper antenna.
If I were in your shoes, I would also consider the Antennacraft HBU 33 from Radio Shack as a possible solution. If it doesn't help, you can always return it for a full refund.