I wanted to wait, but couldn't resist to buy a Chromecast Audio to try. If it's good for the purpose I want, I'll order another one. Together with the recently ordered new Chromecast for the TV, I have 3 rooms covered.
If everything is here I'll try to integrate my FireTV, too. Should be working at least for local audio streaming via Plex or something like it.
And to connect the CCA to the speaker, I also ordered these little mini amplifier from Amazon. Lepai has some acceptable quality for this purpose and doesn't use much space.
And now I have to wait... oh dear.