Apple TV to airplay out of sync

Hey!

I have an issue with my Apple tv (4th gen). I am rerouting all off the sound output to airport express (old one) and it kind of works for most things. I can't seem to get the sound while mirroring from my computer to play on the airplay speakers.

But what is the biggest issue is that both Netflix and Youtube from Apple TV are a bit out of sync. Considering that a similar set up worked fine while playing from my computer I don't know if this is some sort of bug or setting problem. Even though there is no sync adjustment on ATV. Mind that I am using a projector and not TV. So the airplay is quite an important feature for me.