The surround sound setting works fine on my Fire TV cube (3rd gen) in both Auto/Enabled modes connected to my Samsung HDTV/Sony 7.1 amplifier.
However, on the Google TV app, this setting only worked in Enable mode and not Auto mode connected to the Samsung HDTV/Sony 7.1 amplifier combination. And, on the Google TV app with this setting Enabled, there is a slight audio delay to provide the surround sound audio feed that doesn’t happen on the Fire TV app.
Also, on both Fire TV and Google TV apps, whenever I select the Live listing feature to ‘filter by type’ to my Favorite Channels (I have 4 channels), the rendered guide listing doesn’t show guide information on the bottom two listings the first time I try, and when I toggle it again a second time, only the last channel doesn’t show any guide information. Update: Adding the Roku app to this issue since the Roku doesn’t show any guide information when selecting the filter to my Favorite Channels.