Hi RehabMan,
Thank you very much for your guide! Using your instructions I've installed High Sierra on my desktop successfully.
There is only one problem - Intel RAID.
I've disabled RAID for the installation, I mean changed to AHCI, then installed High Sierra on a HDD (which is not a part of RAID).
After added SATA-RAID-unsupported.kext from your guide using "sudo cp -R SATA-RAID-unsupported.kext /Library/Extensions" & "sudo kextcache -i /" commands.
Then rebooted once again, checked System Report/Extension, found this kext (BTW could you please change it's name from "Unsupported" to something else?).
Then rebooted into BIOS to switch back to RAID and I cannot boot into macOS anymore.
Could you please advise how to solve it? Where is my mistake in installation?
Thank you in advance!