THANK YOU! THANK YOU! THANK YOU!
I was ready to give this up as one of those unsolvable computer problems.
For anyone following this thread, one simple solution: in Device Manager disable Intel Display Audio, scan the computer and select High Definition Audio Device.
Once that's done, HDMI is a playback choice.
For me: I plugged the HDMI cable in and the HDMI generic was replaced with Philips (my tv). I had to select it as the default device. It doesn't switch immediately as it does on the other netbook but that's minor. I tested with a short video I have and the sound comes through the tv.
