What is the model number on your Apple TV? IIRC, there are two editions. The newer one with wireless N and "HD" ability, and the original model with wireless G and "DVD" quality. PLEASE CORRECT ME IF I AM WRONG.

That said, You may need to adjust your wireless encryption settings on the DIR-655. There is a setting that aloows you to use WPA *and* WPA2 simultaneously. Some devices don't like this and will refuse to work (e.g. some older Playstation 3 & Xbox 360s). You may have to adjust it to either WPA2 *or* WPA, not both.
Then try again. Without knowing more about your hardware I can't speak with certainty, just my instinct.