But, but, but... Check out the signal strengths available before obstructions! One check and one suggestion:
Is the Terk pointed east? (have to ask) if so, then...
Bypass the distribution amp and connect just one outlet to the cable from the antenna. Before you mentioned the local obstructions, I was thinking you might be overloading the amp even after 100 feet of cable. You have nine signals with noise margins of 60+!
For a DIY, try the bowtie array documented at http://m4antenna.eastmasonvilleweather.com/index.html. It's pretty easy to build and is easy to work with in the attic. Be prepared to try adjusting the antenna's aim if pointing east doesn't work.