ok, then keep using your chromecast.

no, but then you want something like this https://github.com/rgerganov/shanocast

You use it as an input for something like snapcast.

You can get standalone Bluetooth devices that just output audio.

but honestly, the place where Nix “3rd party” tooling shines is in documentation.

totally amazing what can be done with millions of dollars in VC money, huh?

well then life just substantially improved for you.

Why are you not using the options search at https://search.nixos.org/ ? Or an LSP that shows you options in your editor.