I have just got a BT TV Box Pro which is connected to a Sony TV (Model XF9005) by HDMI and a Sonos Beam soundbar connected to the TV by ARC. Generally I am pleased with the TV box. However, when set to surround sound there is a lip sync issue which makes it unwatchable. I am guessing that that is because the TV box cannot process the sound fast enough so that there is nothing to be done, but I would love to be corrected.
You can adjust the box's sound delay from the sound settings in the BT box's menu. I find sound sync an absolute nightmare across the myriad of devices that I use; wish someone would introduce a standard for dealing with this problem in the AV industry.
Anyhoo, someone might be along with some sage advice, shortly...