Marvel controller and SATA mode are both set to IDE.
The ISO firmware update was burned to two disks using different software - to be certain that they were good, and further verified for integrity.
Two optical drives are installed - a DVD RW and a CD RW. Both were tried (with the ISO the only disc in either drive at the time.)
The resultant DOS screen...
Cannot open CD-ROM device "CDROM001"
CDR cache will not stay resident
SHSUCDX can't install
Unable to find CD-ROM drive
The drive is definitely active in the system, as the Windows 7 install disc loads perfectly. The two drives are available via the BIOS and in Windows 7.
Where have I failed?