Hi James, I made no further attempts on the Gigabyte boards; XP 32-bit runs really well on them, so that's where those have long stood. Likewise, I moved my MSI Z97 PC Mate on to other things way back. The driver I used was BWC’s 8.9d AHCI; I don't think driver version 11.2.0.1006 will work on W2K Pro, although it works fine with XP on my Gigabyte boards. I don't know why it does not work on your Gigabyte board.
The trick with W2K Pro and AHCI is using an installation disc that has BWC's Extended Kernel integrated, thus the HFSLIP package tomasz86 made. Though layering BWC's kernel versions is not ideal, after installation you can update to a newer Extended Kernel version.
The latest chipset I tried with Windows 2K Pro is the ASRock X99, where all is well. I have a couple of huge Lian Li PC-V1000L cases moving lots of air with different operating systems on individual NVMe and SSD drives. If I want to change operating systems I just power up, stop at the BIOS and make my selection.
If I try the Z97 again it will probably be on a ASRock Z97 Anniversary board that is currently running XP Pro 64-bit. I very much like that platform and miss not having a Windows 2000 Professional operating system there. I would also like to attempt post-facto switch over from IDE to AHCI to avoid running one extended kernel version atop another.