Just a heads up as these boxes are becoming standard. I have quite a few clients that either had a forced upgrade or new install and most of them had a significant audio delay on Fios, be it Sonos, soundbar or AVR. After spending hours between jobs pulling my hair out I finally figured out the fix. This is a known issue with these boxes, yet Verizon refuses to fix them. Out of desperation I dug into the secret menu of them and found the fix!

Press the power button on the remote once and the ok button twice in (rapid succession) -This will bring up the menu (white and generic)

press the LEFT button on the arrow pad.

This brings up selection of 4 options

Select USER settings

Select HDMI Settings

Select HDMI Audio

Use the keypad and select L-PCM, press OK then back out, this fixes the delay!

It cannot be set to auto. Don't bother adjusting the delays in your receivers or TV's because the delay will follow the other devices (game consoles, streaming devices, etc)