Does 3311 automatically select the audio format

The 3311, like (almost?) all digital receivers, will play whatever you send it as long as it's a supported type. So that will be whatever the default track is on the disc or whatever, unless you manually change it to a different track. Some DVD/BD/Media players allow you to set defaults to certain types or languages of tracks, but that varies per brand/model and is unrelated to your receiver.
Edited by DonoMan - 8/15/12 at 12:53pm

It has nothing to do with the receiver. Your Denon will accept whatever compatible format is being sent to it.

Most blu ray movies default to the DTS-MA or TrueHD soundtrack automatically but on occasion you will find a movie where you have to select the HD soundtrack manually. The Dark Knight is one of those movies. It defaults to Dolby Digital 5.1 instead of TrueHD. You have to select the TrueHD soundtrack.