Assuming that the AirPort Exremes are configured correctly, the "remote" Extreme will "extend" or "repeat" the wireless signal from the main Extreme with the benefit being stronger and faster wireless performance in the remote area.
When you extend using wireless, the ideal location for an extending device is a point that is about half way between the main AirPort and the general area that needs more wireless coverage. In other words, you would want to locate the "remote" Extreme about half way between the main Extreme and the Apple TV.
You may need to experiment a bit with the location of the remote Exteme due to obstrucitons like walls and ceilings in the signal path, which will absorb the signal and slow it down.
For that reason....Ideally....you would connect the two AirPort Extremes together using a wired Ethernet connection, since there is no signal loss in a wire.