The first question is how did you connect the TV's?
There are several different outputs available on the back of the Box
If you are using S-VHS, Coax, or Composite Video to connect to the TV, these are not HD outputs. For HD output, you need to be connected either via HDMI or Component Cables. The next step is to make sure your box is actually configured to output HD.
Go to Menu>Settings>Video Settings on your box, and make sure it is set to either 1080i or 720p.
Hope that helps