In order to take advantage of movies and TV shows in 5.1 surround sound, you must:
1. Have a TV or AV receiver capable of decoding Dolby Digital.
2. Connect your Roku player to your TV or AV receiver using HDMI or optical audio cables.
3. Have a broadband connection of at least 3.5 Mbps. (5.0 or greater is recommended for the best experience.)
If your setup meets these requirements, then, from the Roku home screen, select Settings > Audio mode > 5.1 surround sound.
Note: Currently, only Amazon Video On Demand streams in 5.1 surround sound. Programs that offer 5.1 surround sound can be identified by a "5.1" icon displayed near the parental guidance ratings on movie and TV show detail pages in the Amazon Video On Demand channel.