I have two of these, and they accumulate dust on the back of two high end TVs.
There is no audio passthrough for Plex (same for Kodi).
The PCM output (that the Apple TV loves) sounds like mud through my Sonos speakers. This may be the fault of the Sonos, but I don't care, the dreadful Apple TV box remains unused.
I have an Nvidia Shield Pro, but while the audio is perfect, the frame rate issues are horrible.
Also, the Apple TV has a colour tint on all output formats other than RGB high. You can see it, and the calibrator can definitely see it!
Although the interface is slow, the inbuilt apps on my Sony TVs are better than both streamers.