Hi. Question - can you hear audio on the TV when your receiver is not in standby mode? If not, then I believe that's the issue.
Check out
this thread from yesterday and today. You might need to change a menu option on your TV to get audio over HDMI.
On page 116 of your Yamaha owner's manual, there are some things that you may need to change. Under "Audio Output," you'll want to set "OUT1" and/or "OUT2" (depending on which one(s) that you're using) to "On." You may or may not need to turn "HDMI Control" to "Off" (I just don't know).