My solution is far from ideal but it works for me.

I have a Chromecast connected to my TV which outputs to my stereo system. Power to TV and stereo are controlled via smart plugs that I can quickly toggle when I want to stream music.

The good thing: It works.

The bad things:

• You have to connect navidrome to symfonium using the IP address and not a hostname when using a basic chromecast since that one has a hardcoded dns server. The Chromecast with google TV allows setting a dns server yourself but you loose software volume control through your phone.
• No volume control except directly on the stereo system. This wasn’t an issue with the basic chromecast but it is now with the better one…
• For some reason some songs crash the casting to the chromecast. Again this wasn’t an issue on the cheap Chromecast for some stupid reason