Chromecast and external DAC

I use a few of them, both with their analogue output (into an older high end amplifier in the main system) and a modern more modest amplifier with digital optical input in the bedroom. It does not have a usb output, only mini optical and analogue (mini headphone style plug).
Even the analogue output from the modest internal DAC sounds fine in my main system with Quad electrostats, streaming Qobuz 16/44. See here for measurements that do confirm this favourable impression. The optical digital output is also clean insofar as the modest bedroom system allows me to tell. See here for measurements: http://archimago.blogspot.nl/2016/02/measurements-google-chromecast-audio_27.html
If your wifi is not that good, there is an ethernet adapter for a wired connection.

just got a chromecast and am using it (through its mini optical) with a mf vdac--as willemj states its digital output is very clean and noticeably better than the not-bad analogue output. if you already have an optical cable, a mini adapter costs about $3. i also tried an amazon echo, which is bluetooth/analogue connection and much inferior, though fun to yell at

I've used mine with a Bifrost Multibit and it sounds great. The CA is an audiophile bargain IMO. I use a nice glass fiber Lifatec Mini Toslink/Toslink cable:

http://www.lifatec.com/toslink2.html