With the 91XG and the YA1713 you are pretty much at the end of the rope. Beyond that , you are getting into antenna stacking like stacking like stacking 2 , 8 bay bow tie antennas and quad stacks of YA1713 type antennas and quad stacks of UHF antennas , and the dollar amount goes into a steep climb. There are DX web sites for this sort of thing , Tv and Radio Dxing. DX means D= Distance and X= Unknown. Here are commercial antennas ,
http://forum.tvfool.com/showthread.php?t=491