I would also monitor your systems RAM usage. Make sure you have at least 1/4 of free space on your boot drive (internal SSD drive). In some cases your system may have resource issues. The last issue with out of sync sound can be the codec being used, make sure you have the latest version. If your second Cinema display also has speakers make sure they are disabled. I would suggest that there is a setting and or graphics output configuration issue occurring on the GA-Z77X-UP4 TH, I would double check the firmware settings and make sure. They will also work with thunderbolt Macs (as the last device in chain). Make sure you've directed the sound output correctly by checking your Pref settings. 27 Cinema Display mini display port will work with older Macs with mini display port only output. If you are using external speakers then you'll want to then use the USB port off of the display not the system to drive them.
You should only have the displayPort connection of the display which has speakers.
So what happens here is your sound is taking a different route to the speakers which is slower! Which is why the sync is off between the mouth movement and the voice. So when you have a USB connection in addition to the displayPort's you've confused your computer which path to send the sound through!
First your displays speakers (f you have the newer Cinema display) are feed from the displayPort connection via the Thunderbolt port off your system.
