HTddw670 play only 3.1

The problem sounds like it is the dvd player, have you set-up the audio output menu on the dvd players setup menu? Some dvd units default to a 2 channel stereo output, what is required is you need to enter the setuo menu and enable a dolby digital 5.1 output or the DTS/Bitsteam audio output option. Also be sure to use a digital signal cable connection.