Just a heads-up: until recently, I used both the main and the audio-only HDMI outputs on my x700. I wanted TrueHD with Atmos to be carried directly to my AVR while the video passed directly to the TV. At that time, the TV would not pass properly over eARC (2-channels instead of 8) the audio signal to the AVR. There seemed to be CEC issues with my AVR when using both HDMI outputs. I recently modified my TV's EDID table to allow all 8-channel of audio to pass through to the AVR. As it was no longer needed, I removed the audio-only HDMI connection's cable from the x700 to my AVR. No more CEC issues.
LG OLED55C9, Firmware v04.80.03 | Denon AVR-X3400H, Firmware v7600-8281-6432-2065 | ATV 4K | Sony UBP-X700 | Hsu HC-1 MK2 (C) & HB-1 MK2 (LRSur), Sub VTF-15H MK2, ELAC Atmos | X-Rite i1D3 OEM | 2019 CalMAN Home for LG