> I wish Google could publish server software for Win10 so that I could cast to that as a Chromecast target rather than go via the Chromecast Audio. However I understand there's probably DRM reasons why efforts for this to happen were shut down.

Audio-only Cast devices do not support DRM, so I don't know why audio casting to a desktop PC would be stopped by DRM concerns.

https://developers.google.com/cast/docs/audio