Apple TV volume goes low when playing Dolby Digital or Atoms Content
The volume of my Apple TV goes very low while playing Dolby Digital (5.1) or Atoms or Multichannel PCM Content but goes to normal while playing a Stereo content.
Cinematic content may accommodate for a much larger audio dynamic range, resulting in regular conversation being lower on the volume scale compared to the maximum output, to allow for loud sounds being much louder. This is as expected and as intended.