I recently experienced huge (> 400 ms) audio delay with a YAS-306 sound bar when connected to a TV using the supplied Optical audio cable.
After updating the YAS-306 firmware (via MusicCast app) and checking the TV audio settings, I identified the root cause of the problem.
The problem seems to be caused by multi-room being enabled (Two Yamaha devices are linked). Then applying a solution is simple : disable multi-room link when watching TV.
To test the result or identify your lag, use this great Twitch video on youtube.
Here’s a link the device owner’s manual which shows how to setup audio delay with the remote.
I contacted Yamaha support on May 19th 2018 about the matter.