I was looking for a Squeezebox replacement since my device died and they stopped making it. I really didn't want to build out a dedicated PC or Raspberry solution just for audio, so was making do with Roku for audio (it acutally has a surprisingly large number of audio streaming services - it even covers my local FM radio channels).
Tried the first Chromecast - and it was largely a "meh" experience. Video was grainy and choppy and audio sounded quite substandard. For example the same youtube audio or internet audio would sound much better when streamed from the Roku channel than when casted from Chromecast.
Took another gamble at the new Chromecast Audio - and it is a phenomenal device. It actually plays as well as my Squeezebox. For $35, you get really high quality audio, and it has digital out so you can connect it to a DAC, or optionally use its inbuilt DAC which is not bad at all. Some people are even using it to drive moderately hard to drive headphones. It also supports high res audio up to 24/96. The really neat thing is that if you cast Spotify or Pandora from your phone to the CCA device, it will stream directly from Spotify after the initial handshake and will not stream through your phone. All in all, I can't imagine how they pulled off this quality of audio output and features for $35.