> Booted to rescue mode again and found that /proc/irq/11 contained an
> empty directory named "ahci".
> lspci shows all the expected devices.


AHCI? Isn't that for SATA settings? What are the SATA settings in the BIOS
set to for SATA?Have you tried changing them?

>
> Did it all over again with a regular ATA DVD/CD drive and the SATA
> unit removed from the system.


Did you disable the SATA controller on the motherboard or just disconnect
the SATA device?

>Nothing changed. So I do not think we
> can blame this on read errors on the optical drive. I used this same
> set of
> CDs to install on another PC a few weeks ago and that one worked fine,
> so they probably are not bad,


Also try using the noirqpoll kernel option while booting.