I had no idea what audio the ChromeCast dongle put out though there was talk that it could do everything from stereo through 5.1 (Netflix)

In any case, I purchased an AGPtek audio extractor from Amazon and am happy to report it works flawlessly with every app that I was interested in that supported casting!

It was more than I had wanted to pay for a device of this sort but cheaper than buying a new HDMI capable receiver