I'm assuming you have a 4520 driving them. First, the stupid questions! Double check ALL speaker connections at the speaker and the AVR. Make sure the speakers are not out of phase, or the red, positive on the speaker is connected to the red or positive at the avr for all speakers. Next, how are the disc players connected to the avr? Analog or digital?
Next, since you have 2 dvd players connected at the same time, then they can't be employed using the same source on the AVR. One has to be DVD Player, and the other, Bluray Player, or CD player selection on the AVR. Perhaps you could post how you have them connected so we get an idea.
Next, what soundfield mode is the AVR in when playing the music? If you look at the 4520 remote, near the bottom you will see 4 buttons in color. You should hold down the red button until a big menu window appears on screen, then select stereo. Or, if you have the disc players connected via analog cables, use the yellow "Direct" button so the Denon keeps the signal in analog and does not process it.
Just some ideas to check.
Last edited by audio4life; 07-05-2015 at 12:00 PM.