Ok so it seems I made progress and managed to work through the 66 error by using
@ASentientBot and
@libneko guides. Thanks a lot for coming up with that.
@jackluke I was able to also go through the kext installation process afterwards too. And on a first glance all looks well, however after reboot, Audio situation is still the same - as if the kext is not installed properly (there is no option for Audio in system preferences)...
Catalina worked with the same kexts, so another approach might be needed here.
Just for clarity - I installed using OpenCore method (configuration very similar to the one that your tool creates) and I boot using opencore too (easier for me because of the display firing up only during the macOS loading)