If you ave difficulty in the attic, can you consider mounting outside in the clear? Also, if you don't succeed in getting adequate reception with a single antenna, you can feed each HDHR from a different antenna.
I like my HDHR tuners, both the new HDHR3-US and the older HDHR-US...
http://forum.tvfool.com/showthread.php?t=820 Use the configuration utility to manually tune to the real channels and see signal strength and quality in real time, a great antenna aiming aid, no tuner rescan needed between adjustments to the antenna aim.