Maybe what you need is one of these to extract audio from the Chromecast with Google TV?
www.audiosciencereview.com

Amazon Basics 4K HDMI Extractor Review
This is a review and detailed measurements of the Amazon Basics 4K HDMI extractor. Member kindly purchased and drop shipped it to me. It normally costs $22.89 but was on sale for just $5!!! The case is the standard metal one for these kinds of adapters. Power is provided with a supplied USB-A...
