Denon DVD and Receiver

I've got a Denon DVD player and Denon Receiever (AVR 3800).
When playing the DVD, I have to turn up the volume several notches to match the output of other sources coming through the receiver. I was using an opitical cable on the DVD player, but changed over to high quality coaxial cable, but to no effect. Anybody have any ideas?

P.S. The gain settings for analogue on the receiver have been set to zero
There is no reason why the volume level when playing a DVD should be exactly the same as other sources. For one thing, the volume level will depend on how the disc was recorded. A disc might be recoreded "softly" so as to leave room (with the available number of bits) for loud dynamic peaks. Conversely, a disc might be recorded "loud" for improved resolution of quiet passages, but this would require greater limiting of the peaks.

Don't worry about turning up the volume. What you really are doing is attenuating the signal less. Ideally, the volume control would be all the way up, and/or removed entirely from the circuit.
Just an idea, I have a 3600. Did you accidently turn down the souce input on the remote? My receiver has - & + gain for the input signal. You could increase this instead of volume too.
When I first got the DVD player, the volume levels were similar compared to other sources. It just seems lately that the volume has dropped on the DVD player playing the same DVD's.

The AVR 3800 receiver does in fact a source input for analogue inputs, like I said in my post those are set to zero gain.