The Netflix client app that runs on the Telus STB was probably written by an app dev. company that specializes in Mediaroom apps, either on contract to Telus or on their own with the expectation to market it to other Mediaroom providers.
If it's not a problem with the Netflix interface or servers, it could be a bug, a limitation of the Mediaroom API or infrastructure, or a limitation of the STB hardware. Even though the STB supports surround sound for TV signals, I think the data access APIs were designed for supplementary data, not for full-fledged streaming.
That said, if surround sound is important to you, I would initiate a formal trouble ticket with a tracking number (or whatever terminology Telus uses). It would probably help if you could confirm that the movie plays in surround sound on other hardware when you call them.
Last edited by Dr.Dave; 2015-11-29 at 10:04 AM.