Yes, the Roku player can support pass-through of 5.1 surround sound to your TV or AV receiver. Currently, only Netflix and Amazon Instant Video offers content in 5.1 surround sound, typically on HD movies and TV shows.
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 Netflix and Amazon channels. We expect other partners to add support for 5.1 surround sound in the future.
Note: 5.1 surround sound with Netflix on Roku 2 and Roku LT players requires a receiver capable of decoding Dolby Digital Plus.