I think the first thing you should do is check to ensure that your Beam is receiving a Dolby Digital signal. While watching something on your TV, open up the controller app, and go to ...More and then Settings. Click on "About My Sonos System" and look underneath the section talking about your Beam for the line that says "Audio In:" and let us know what you see there.
You can adjust the emphasis of the voice by turning on
speech enhancement, and you can also reduce the volume of the surrounds by going into the room settings for the Beam, clicking on Advanced Audio, then Surround Settings, and using the volume slider.