I had the same problem.
I figured out why it was not working. Hope this helps everyone else.
Page 34 of the Yamaha's manual discusses how to turn on the ARC setting and the CEC setting on the soundbar. My ARC setting was turned off out of the box.
Basically, Turn off the Yamaha. Then, while off, hold down the surround button for three seconds. One light should glow and the unit should then turn on.
To disable, just repeat.
To enable CEC, turn off the Yamaha. Then, while off, hold down the HDMI button for three seconds.
Hope that helps everyone else having this conundrum!