Sound sounds better when it's coming from more directions. Okay, that may not be entirely how audio works, but I never claimed to be an expert in the area. I can say this. When an explosion happens to your left on screen and you hear it come that direction, it's very cool. That's an objective statement of fact.
Since this is the case, Google has added Dolby Digital Plus surround sound support to Android TV and Roku. You can also get immersive audio via Chromecast if the dongle is hooked into an A/V receiver that supports 5 channel PCM input.
Play Movies now support @Dolby Digital Plus surround sound on Android TV & Roku!
— Google Play (@GooglePlay) May 4, 2016
You may think that a video streaming service would handle surround sound from the get go. You would be wrong. Netflix didn't add support until basically a year ago.
This doesn't magically make everything you watch sound better. The movie or show that you're watching must explicitly support Dolby Digital Plus 5.1 as well. Much of the content is stereo only. But with the right movie, you're good to go.