First Impressions:

Google has delivered on it's multi-room audio for their Chromecast Audio device (currently 2 for $55 at the Play store) Jury is still out if it will ever work with the regular Chromecasts but it definitely works with Chromecast Audio and works well. No sync or skip issues in my 4 hour test.

Some minor issues though:

1.) If any Chromecast Audio in the group gets disconnected, the music stops until it reconnects. Something to keep in mind if you decide to unplug & move a speaker while music is playing.

2.) Currently seeing bug in which only 2 of my 3 CC Audios show up as part of the group on my phone but all 3 are still playing music. (this could be because I unplugged the Jambox and plugged it back in...)

3.) Looks like there is individual volume control for each CCA from the phone app but this isn't working for me at the moment. You can still physically adjust each speaker of course. Simultaneous volume control from the phone works.

If you plan to purchase satellite speakers specifically for a CC Audio setup, I'd recommend looking for something that also has a regular USB port to power the CC Audio. This way you don't need two power cords at each speaker and you have the option of going completely wireless if you have battery powered speakers. My Klipsch KMC1 (as low as $79 on woot recently or about $120 most other places.) has a USB port and will run for about 10-11 hours at party volume on battery with Chromecast attached. The Big Jam Box on the other hand does not have a USB port.

Also having now listened to the Jam Box and KMC1 side by side playing the same thing, the Klipsch is far superior to my ears. Much better bass. I'm going to grab another if I see the $79 offer again.