Cannot get ARC/eARC working with LG C9 and Onkyo RZ720?? Help Please

Hi All,

I need some help. I cannot get ARC or eARC working with my setup.

This is my current setup:

PC:
AMD 5900X
Gigabyte X570 Aourus Master
32Gb Ram
GeForce RTX 2080 Ti GAMING X TRIO (HDMI 2.0b) ? Nvidia V461.40 21-01-21
XFX Radeon RX 6900 XT Speedster MERC319 Black (HDMI 2.1) - Adrenalin 2020 Edition 21.1.1
Windows 10 ? 20H2 OS Build 19042.746

Home Theatre:
Onkyo TX-RZ720 ? Firmware 1141-8020-3070-0011 - 14/01/21 ? I believe they did a firmware update to enable eARC, But cant get ARC either.

Android TVBox:
MeCool KM1 Collective v9 Nov 5 2019 (HDMI 2.1)

TV:
LG 55 C9 - OLED55C9PVA - 05.00.03 (HDMI 2.1)

I have tried using the Nvidia RTX2080Ti(HDMI 2.0b), then purchased an AMD RX6900XT(HDMI 2.1) as I am wandering whether the HDMI version have something to do with it. I am trying to setup a 5.1.2 setup(Atmos using height speakers)

I have tried the following:
- I have connected my PC directly to the LG HDMI 1 Port using an HDMI 2.1 cable.
- Then connected LG HDMI 2(eARC) to the Onkyo Main(Arc) HDMI port using a HDMI 2.1 cable.
- Then connected Android TVBox to LG HDMI 3



LG TV Settings:
/Sound /Sound Out /HDMI ARC /Digital Sound Output - Pass Through
                                                                                        /eARC - Off
        /Additional Settings /DTV Audio Setting - Auto
                /AV Sync Adjust - Off
                /HDMI Input Audio /HDMI 1 - PCM
                        /HDMI 2 - PCM
                        /HDMI 3 - PCM
                        /HDMI 4 - PCM
/Connection /HDMI Device Settings /Auto Device Detection - Off
                        /Simplink(HDMI-CEC) - On
                        /Auto Power Sync - On

Windows 10:
Left clicked on the speaker in the System tray and select ?LG TV (AMD High Definition Audio Device)?

Onkyo Settings:
1-Input/Output Assign /1-TV Out/OSD - HDMI Out - Main+Sub
                                                                - Dolby Vision - Off
                                                                - OSD Language - English
                                                                - Impose OSD - On
                                                                - Mini Player OSD - Always On
                                                                - Screen Saver - 5 Minutes
                /2-HDMI Input - BD/DVD CBL/SAT Game STRM/BOX     PC CD TV
                        HDMI1 HDMI2 HDMI4 HDMI3          HDMI5 - -
                                        /3-Video Input - BD/DVD CBL/SAT Game STRM/BOX     PC CD TV
                        - - -         -     -         - -
                                        /4-Digital Audio - BD/DVD CBL/SAT Game STRM/BOX     PC CD TV
                        - - -         -     -         - -
                                        /5-Analog Input - BD/DVD CBL/SAT Game STRM/BOX     PC CD TV
                        - - -         -     -         - -
5-Hardware - 1 HDMI - HDMI CEC - Off
                        - HDMI - Last
                        - Audio TV Out - Off
                        - ARC - - (Greyed out)
                        - Auto Lip Sync - ON


So? What am I doing wrong? Please can you refer me to some resources or advise me what to do with this setup. It does not work with Both my PC and Android Box. Stumped!