Google Chromecast Audio works perfectly with Focus XD. We suggest using an optical digital connection between Google Chromecast Audio and Hub / Connect. Set up your Google Chromecast Audio as per instructions provided and use a Mini-TOSlink to TOSlink cable (not included) to connect to the optical input of Hub / Connect.
If using an analog connection we recommend activating the Full Dynamic Range setting in the Google Chromecast Audio settings, read more on the Google Chromecast Audio help page here.