How to get best sound

[beid25]

Hi all,

I have a Denon AVR-591 and a Sony model DVP-NC85h 5 disc DVD changer. It seems no matter what setting I choose on the DVD player my Denon is always outputting the sound as PL II C. I was wondering what the best audio setting would be in order to get the movies to output in Dolby Digital. Any help would be appreciated and thanks.