XP Pro Repair Install says: "No disk drives found", but this is NOT the usual driver issue

XP Pro Repair Install says: "No disk drives found", but this is NOT the
usual driver issue

I've seen hundreds of complaints/questions relating to the fairly common
problem of getting the "Setup did not find any hard disk drives installed
in your computer" message while trying to install (or Repair Install)
Windows XP. But in every single one I've seen, the problem turns out to be
a simple issue of XP not having the correct driver(s) for the disk
controller in question.
This is NOT one of those cases!
First, the disk controller in this case is an Adaptec SCSI-320 RAID
controller, the latest drivers for which I've always included on the
Install/Repair Install disk using nLite in advance. Even so, I've also
always had a floppy disk with the same drivers on it that I can optionally
supply after pressing F6 and then loading it from the floppy (although
Windows always complains that the F6 drivers are redundant since it
already has the correct drivers built in (via nLite). I've alternated
between forcing the Windows installer to use the F6 drivers anyway, or
allowing the installer to continue with the drivers it already has, but in
either case it still always complains that "Setup did not find any hard
disk drives installed in your computer".
By the way, I've frequently confirmed that both sets of drivers are
bit-for-bit identical, and that they are the latest versions for XP SP3
(there are newer drivers for later operating systems, but I scrupulously
avoid using them). Also, since I can examine the files on the XP Pro
installation I previously successfully installed on that system (note that
I'm trying a Repair Install, not a new fresh install), I've also confirmed
that the drivers already on the system are bit-for-bit identical with the
drivers on both the F6 floppy and the Repair Install boot CD.
The system in question is home-built (I'm a very experienced user who is
also a programmer). It's running 32-bit XP Pro/SP3 with all Windows
updates and patches. The Adaptec controller is setup in HostRaid mode, and
everything about both the controller and the two RAID-0 drives are seen
perfectly in the BIOS. And when I run a Live CD, everything on the system
partition looks and works perfectly.
The purpose of all that verbiage is to try to convince you that this is
NOT a driver problem, but instead something more complicated and difficult
that I cannot fathom or correct. Does anyone know what, exactly, causes
Windows Setup to think there are no disk drives in the system even when
there clearly ARE? Note that if I enter into the repair console, Windows
sees the SCSI system disk perfectly well!
This is a tough one, folks! Can anyone offer any suggestions or assistance
please?
Thanks!