Apple TV Streaming Sound Quality vs Streamer?

This means you are already using Apple AirPlay.  As I mentioned, there are better AirPlay sources than the Apple TV, especially for music.  The network can also make a difference.

Apple TV streaming sounds really poor. I was excited to get the Tidal app on it but it just sounds poor via hdmi into an Arcam AVR 850. Ok for tv but not for audio. 

Apple TV with the Tidal app sounds fantastic IMO.

Tidal is only CD quality after all.

I use the Sony TV optical digital out to a Gungnir Multibit D/A converter into my audio system and get great TV, BluRay, and audio playback from my iMac SSD.

Curious why you say Tidal is only cd quality after all?
Or are you of the opinion, as some are, that the MQA titles do not offer any improvement over 16/44 redbook content?
Just my 2 cents but I can hear a considerable difference on some MQA titles compared to the "regular" 16/44 stream offered on Tidal.
But a lot of that could be the rest of my system, who knows?

ATV Gen 3 doesn't TIDAL APP. Gen has Tidal but without optical out. You would need a good DAC to sound better from ATV.