The manual does note that jumper points are provided for clearing CMOS, which usually means that removing the battery isn't by itself a really reliable way of clearing settings. If you unplug power, and put a jumper between the two solder points indicated, the CMOS should clear (without removing the battery? – see bottom of page 13).
Nothing startling at the ASRock BIOS downloads that I can see. The BIOS notes on BIOS Update presumedly were followed.
(I'll note that the comment in how to update your BIOS – " if the problem still persists, update the original BIOS file" – is a bit vague, and doesn't mention that you might wish to have the BIOS download for your previous BIOS version handy and loaded to a floppy before you start installing an update.)
Just above the BIOS download offerings, on the same page, there's a list of Drivers available specific to the motherboard. The only real "OS dependency" is for AMR devices, which would be of interest only if you're using a voice-over-IP (VOIP) or other voice modulation telephony device. Each of the listed OS versions does require a specific and different AMR driver. There are some differences in USB drivers, but I don't see them as likely to interfere with the basic OS installation(s).
You may have tried the "Sea Tools Diagnostic" download or used the online version. I've found either to be reliable, although there are a few problems that the diagnostics admit can't be reliably tagged. I believe they quote "98% reliable" for their testing.
I'll guess that you're using the "DiskWizard Installation Tool" for your reformats. (An excellent tool for anyone using Seagate drives.)
You've almost certainly seen the Seagate Low Level Format FAQ, since you've referred to using the "Zero Fill" mode for your reformats.
The only thing of note there is that a "Zero Fill (Quick)" will erase everything on the drive, but doesn't write to all available sectors, so it may not find and mark defective sectors. Since it obliterates the boot sector and low clusters, it may erase a "sector-exclude" record there, resulting later in the drive trying to write to scabby spots on the disks. The OS itself should find any defects when it tries to write to one – and should automatically mark the sector and go elsewhere, so this shouldn't be a problem.
"Zero Fill Drive (Full) will write over the entire data area of the drive. This is useful if a drive has bad sectors that cannot be fixed by the operating system. This will also erase all the data on the drive, but it will take several hours." (italics added)
The symptoms described don't sound like bad writes to disk but it's a thought to be kept for recall if nothing else comes up.
Hopefully, we're not too far apart on what's been done?