It could just be a simple setting, but there might be something that requires a little more troubleshooting happening ...

Hidden Roku menus help you fix issues and tweak your setup fast. You can organize apps, watchlists, and remotes way better ...

Check the audio settings of the Roku. If it's not hooked up to a system capable of playing. 5.1, it needs to be set to stereo. What you mean by "downloaded" can make a difference too. It's set for 5.1 ...