With respect to Xfinity, is the audio sync drifting over time while watching the same program without changing anything? I'm wondering if the Xfinity audio and video are actually two separate streams to the cable box. We have a system of several monitors in a bar and their "experts" didn't want to install a proper distribution and control system. Each TV has a dedicated cable box. If you tune all of the TV's to the same channel, the TV's will start more or less synchronized, but over time the displays (both audio and video) will drift several seconds out of sync. Only one TV can be connected to the PA system, else the audio sync would be chaos.

They mostly watch sports play by play and it is difficult to make any comment with respect to drifting voice sync on a given TV, but I wouldn't be surprised if it drifted.