Thank you both for your replies.
No, I haven't traced that cable completely, but I don't think its being combined somewhere along the line. I have separate runs for satellite (inactive) and cable/internet (active) running into the same room that came with the house. When I did the scan previously I unplugged the cable box and left it powered on with the end of the cord next to the TV, so maybe some signal was being picked up.
I removed the CM7777 completely, did a rough bore sighting and reception is more normal. I haven't cross-checked all of the stations but I am receiving much more now and the duplicate channels are gone for the most part. I am receiving duplicates on channel 11 (WTZT, 11.1 through 11.4) with somewhat spotty reception, but this looks to be coming in on VHF high from ~320 degrees. I am picking up Ch 14 (15.1, WHDF) from ~310 degrees with very good reception.
I'm wondering if maybe I could get better results with a 360 degree omni-directional antenna for my area, installed outside at the top of the mast. Something like this:
http://www.solidsignal.com/pview.asp...sku=1579830649
Do you think it would be worth the $50 to try out?