Given that you are only 2 to 4 miles from several full power transmitters, your experience is to be expected. Any amplified antenna would be driven into overload and thus produce less, not more usable signal to the TV. In fact the strong signal level may be enough to overload the TV receiver without any amplification. You are in a situation where 'less can be more'.
Your selection of the Antennas Direct DB-2 is not bad... though I think you can do a bit better yet. Try an
RCA ANT-751 pointed toward 290° on the compass. Also, be prepared to add some
attenuation (15 to 25 dB, est.). You are in a situation where you need clean signal.... that's not
too strong. The ANT-751 will be a bit directional which means it will ignore some reflected signal from the sides. However, it and virtually all other antennas will receive too much signal, which is what the attenuator(s) will give you control over. Most of the stations on azimuth 120° will be received from the back of the antenna... some experimentation with the exact attenuation will help if you are interested in the weaker signals.
The ANT-751 lends itself to outdoor wall mounting, which means you may be able to use the building as a shield from the strongest signals... if needed. Again, some experimentation may be in order.
