I seem to have resolved my audio sync problem. ATV4k running to Marantz NR1607 into LG OLED B6. ATV settings match frame rate on, match dynamic range on, best audio available. AVR settings - video conversion off. TV settings - AV sync on set to bypass. Using public beta tvos12. Was getting lip sync issues with DV content from ATV only - all other content ok inc DV content from tv apps sending sound to AVR via ARC.
I read somewhere that using the HDMI input closest to the output (in my case input 7) can help in Marantz/Denon due to some kind of internal clock issue that I totally don’t understand.
However since doing this and with these settings, the DV content in iTunes and Netflix outputs with no noticeable delay.
Might help someone here. Helped me! I’ll try to find the link to where I read it.
LG OLED55B6, Marantz NR1607 with 5.1.2, ATV 4K, Virgo TiVo, PS4 Pro, Sony UBPX700