And ... at some point in the future ... someone is following these bread crumbs ....
After some googling and reading I followed a thread on a Redhat Forum.
The author was talking about APIC and various issues around the aic7xxx driver.
Then I remembered seeing an option in the BIOS for APIC (Advanced Programmable Interrupt Controller - apparently new mobos have fancy IRQ controllers) which was disabled.
I enabled it.
Now the Adaptec Card is recognised

And so onto backups ...