Judging from the path profiles in your original TVF report (click on the station call sign), going up will buy you far more than any amplifier or antenna upgrade. (That's not to say you won't benefit from an antenna upgrade.)
Given the proximity to KTBW and KCPQ, amplification will likely be overloaded if you get the additional signal I expect.
Experiment with the
Interactive TV Map using different placements of the antenna and mounting height. I think you will see signal levels change significantly with relatively small changes. If I'm wrong, only a few minutes of time spent.
As T.G. mentioned earlier, depending on the HTPC software package you use, you can dedicate individual ports on the HD HomeRun to separate antennas.
Thread 820 That has allowed me to avoid the need for Jointennas.