Sounds like you need to go into the receiver's setup menus, and adjust the volume of each speaker, in the "Levels" area. The ideal way to do this is while using an SPL (Sound Pressure Level) meter and an HT Setup disc (Avia, S&V Tune Up, or DVE/Digital Video Essentials). You can get the SPL meter at Radio Shack and the S&V disc at Best Buy. Amazon.com has the DVE or Avia disc.
Without the SPL meter, you'll just have to do it by ear. Adjust the center channel a little higher than the others, and the background music and noises won't overpower the voices. You can also set the speaker distances too. Set the distance of each speaker, from the "sweet spot" (place you'll be sitting while watching movies or listening to music).
Good luck! Keep us posted on how it works out, and how you like your equipment.
Denon makes good stuff, but have a language of their own. Their remotes aren't the easiest to learn either..........