I just got Showtime for free with Spotify student discount. There's no surround sound on the app on my Shield. Unfortunately I can't use it through Amazon because you have to sign up for it separately.
Is there any version of the app that supports surround? Does the Fire TV app support surround? If it does I can try the apk for that version. I also have an Apple TV 4k.
Nope, and its one of the reason's I dropped Showtime. Starz and HBO have managed to get it to work, Showtime should too. Sorry but I'm not watching movies in stereo.