Have just started using Stream What You Hear and am also experiencing a delay in audio when listening to Video sound tracks.
Easy solution is to use VLC media player and then go to Tools and the Track synchronisation.
I have found that if you put a negative delay of -1.500 seconds that the audio will then sync.
Mute your PC’s audio and then listen only to the SONOS players.
Have also discovered that if you Group your SONOS players and then play to the main grouped player then all SONOS players will play.