I think – no.
I don’t have chromecast audio, so I can’t check it myself.
I’ve read this topic – http://forum.synology.com/enu/viewtopic.php?f=216&t=105339 .
People can’t play frow web-interface of audiostation to chromecast.
So my package also can’t.
Please try it yourself – could you select your chromecast device in audiostation web window, at top buttons bar, in connected sound devices list ?