I recently replaced my Bravia XD93 with a Bravia XR80. Straight swap. 

My Sky Q box is connected to the TV in the HDMI 1 input. It's not a 120hz input but the Sky Q box doesn't output 120hz, so that's fine. No lip sync issues with this set up. 

My UBP-X800M2 4K blu ray player is connected to my TA-AN1000 amp in the BD/DVD input. The amp output is connected to the XR80 via the eARC input. There is a lip sync issue with this connection. I can't currently fathom out why. My HDMI cables are QED and capable spec. As far as I'm aware my gear is compatible. I haven't tried an optical cable, but at the end of the day the eARC with HDMI should work. When I adjust the settings on the amplifier to 130m/s, it looks better, but I don't like having to do that. 

When I play a disc and turn the amp off and have pass through on, the lip sync is fine! It's only when I turn the amp on and output the sound through my 5.1 system. 

I had no problems whatsoever with the XD93. Any thoughts from someone with more knowledge than me would be appreciated. It's a head scratcher.