Your salesguy obviously was misinformed. As close as you are to the towers you shouldn't have a reception problem with the right antenna.
I am using the Sony HD200 STB to receive my signal and it does very well bringing in the stations from my location in Gulf Breeze but I am also using it for DirecTV.
I use a directional antenna as all of the broadcast towers are very near the same compass direction for me. I do use a CM 9521 rotor to adjust the antenna direction by remote control and it is a great little device. Sometimes moving the antenna only 2 degrees can make a big difference for my reception.
To the best of my knowledge antennas aren't really HD compatable. They are either UHF, VHF or both. They can also add radio transmission. Most of the digital stations in our area are UHF. Go to www.antennaweb.org
to determine more. I really like the info at www.100000watts.com
for finding station location and broadcast towers. Make sure to click on the little tower that shows up for each station as it shows a map location for the tower.
You shouldn't need an amplifier that close to the towers but all amplifiers are certainly not created equal. Some have higher gain, higher noise and can be UHF, VHF or both. The CM 7777 is a popular one for both.
Higher is usually better for antenna location. How long is your coax run and what type are using?