Just a warning - at least some non-dumb Hisense tvs are suffering from flash memory corruption rendering the whole tv unusable, since to switch HDMI inputs to use external sources still require Android UI operating. Google "Hisense low memory" - a lot of perfectly fine otherwise tvs turns to electronic junk just because of that.
I believe the current generation of 4k Hisense TV's are now smart tvs - my old hisense (still worked fine, but I wanted a bigger screen) was dumb, the replacement available was a smart.
Not the end of the world - it's still running off an HDMI input from a PC, so the smarts are there, but not doing any damage.
I talked to support a while ago because I needed a replacement. There were none in stock but the agent said they were experiencing a supply shortage, though there are plans to get more TVs onto Amazon and Walmart soon (whenever that is).
Trying to buy an Nvidia Shield has always led to mixed sounding reviews on what I should buy. The number one problem I would really like to solve right now is my Chromecast's chronic inability to output 5.1 audio from streams (sometimes) meaning I can barely hear dialog due to the stereo downmix.
But no one can positively tell me what works, and what doesn't.
Don't have any issues playing 5.1 audio on the shield or my old google tv stick, it might be a problem with the sources you're using. The only time I had an issue was with the AppleTV app refusing to realize a particular show had dolby vision and surround sound available, so I had to force-stop and clear the app's cache and then it worked fine.
I'm not a huge audiophile, but everyone I saw commenting on Reddit said that Plex works amazing on the Shield, with the various audio on their files. I think the primary audio feature they sought was Atmos.