Kexts:
- Try removing FakePCIID.kext and FakePCIID_intel_HDMI_Audio.kext from the /OC/Kexts folder. When using WhateverGreen.kext you shouldn't need these two kexts, especial when your IGPU has been disabled and all graphics are being run through the RX580. The two kexts are not enabled/included in the Kernel > Add section of your config.plist so they can simply be deleted from the /OC/Kexts folder.
- You have SMCSuperIO.kext in your /OC/Kexts folder but do not have an entry in your config.plist for his kext. You may want to add an entry for the SMCSensor.kext, if you are using a Hardware monitoring app.
- You have an entry in your config.plist for SMCLightSensor.kext, which is only required on a laptop with a light sensor, but you do not (fortunately) have the kext in your /OC/Kexts folder. Remove the config.plist entry for this unused kext.
- I would also remove the XHCI-unsupported.kext, as that is not needed with OpenCore, especially when you are using a custom USBPorts.kext. Remember to remove the entry in the config.plist for this kext, as well as removing the kext from the /OC/Kexts folder.
- You have AirportBcrmFixup.kext in your /OC/Kexts folder but it is not mentioned in your config.plist. Do you need this kext?
- You have FakeSMC.kext in your /OC/Kexts folder. You do not need this kext when using VirtualSMC.kext.
IGPU:
I would recommend you enable your Intel GPU in your bios, and then add an Empty/Headless framebuffer to the DeviceProperties section of your config.plist for your HD 530 IGPU.
PciRoot(0x0)/Pci(0x2,0x0) > Data > 01001219
SMBIOS:
You are using an iMac Pro 1,1 SMBIOS with a Skylake system, why? The iMac 17,1 SMBIOS would work perfectly well with your system.
Boot Arguments:
You would need to change the
shikigva=128 boot argument to
shikigva=80 if you do enable the IGPU and use the iMac 17,1 SMBIOS. You should also be aware that none of the shikigva boot arguments work in Big Sur.
OpenCore Version:
You might also want to think about updating the version of OpenCore you are using (0.6.3) to a more recent version.
Drivers:
You have four (4) drivers named in the config.plist, but have seventeen (17) drivers present in the /OC/Drivers folder. A number of which are carried over from an old version of Clover and are absolutely useless in OpenCore. Remove the drivers that are not mentioned in your config.plist.
DSDT.aml
Your config.plist calls a DSDT.aml in the ACPI > Add section, but you do not have a patched DSDT.aml present in your /OC/ACPI folder. I would recommend you remove the DSDT.aml entry from your config.plist.
SSDT:
You have an SSDT from another Hackintosh site in your setup. This contains an amalgamation of a number of common SSDT fixes, not all of which you need and some of which are very generic.
I would recommend you swap this single SSDT for a number of custom SSDT's that can be generated using Corpnewt's SSDTTime python script. The SSDT's for EC, HPET, PLUG and others are generated from your systems DSDT.aml so they only contain the entries for your specific system. Which to my mind is a better solution.
Anyway, I think you have some issues to resolve with your current setup, not just the HDMI Audio you posted about. It think if you amend your OC setup as recommended above then your HDMI Audio issues will be resolved.