[nonninz]

That routes all the audio from the mac though, not only Spotify. And with a noticeable delay.

This makes watching a "GIF" with audio (say browsing Reddit), opening a video, answering a slack call, etc. a very bad experience.

Spotify by itself supports its own protocol, whatever that may be, and chromecast. The iOS app should also support Airplay through the OS.

Personally I have a Spotify enabled receiver plugged to my audio system, it works really well.