I can confirm that that little device no longer works. The old models worked without the VGA portion needing to be plugged in, however the new models shipping from China don't work unless the VGA unit is plugged into something, which basically defeats the purpose.
When I first got my Chromecast, I was beyond frustrated that the music always cut out (even though watching videos was fine). One day, I was determined to get to the bottom of it, and realized that my roommate's Yamaha RX-V571 will reset the HDMI connection every two seconds if it can't handshake the video. He has an HDMI->VGA adaptor and a VGA projector plugged into the same receiver. So, whenever I want to listen to music in our living room, I have to turn his projector on for two seconds. It's beyond stupid, but at least it works.
That's odd, my slightly older Yamaha (RX-V367) works fine with the chromecast as an HDMI device with no tv hooked up. Wonder why the newer model doesn't like it.