Regular Chromecast (Gen 2 and above) can now be added to groups too!
https://chromeunboxed.com/news/chromecast-video-and-smart-di...
https://chromeunboxed.com/news/chromecast-video-and-smart-di...
Be funny if they soon release a new Chromecast that has HDMI and AUX outs; the thing that always confused me about Chromecast Audio was why it needed to be a separate thing, especially after they went to the hockey-puck with a tail rather than stick format for the regular Chromecast.
Edit: meh, no, these things are Energy Star compliant so they shut down if no VGA is connected. And they don't support HDCP.
There's guides for this, works flawlessly.