Problems with NEC optiarc AD 7173 A

Hi

I've just built two near identical pcs based on the Shuttle SN27P2 with NEC AD 7173 A DVD writers (full spec below in my signature).

Both show the same problems that I'm assuming are something to do with the DVD drives;

A known-good* bootable CD (Ultimate Boot CD 3.4) will not boot in either machine, giving the error:
"Error booting from CD/DVD drive
Press any key to reboot
..............80800279"

*confirmed good on 2 other PCs here.

Also, both Age of Mythology Gold and LoTR Battle for Middle Earth II do not install correctly: at the end of installation, you get a "encountered an error and needs to close, sorry for the inconvenience" message.
With AOM, the game seems to work fine anyway.
With LoTR BfME II however, it does not run, saying that a directx file is missing. I have tried copying this file into System32 manually but the game still does not run.

I have read the FAQ on the 7173 drive here and looked through the bios settings for something to tweak with regards the 7173 (PIO settings? but I don't know what these are).
I'm not even certain that all the above are symptoms of the same problem or that this is with the 7173.
I am at a bit of a loss now though and any help with diagnosis or cure would be very much appreciated.

Thanks for reading....

By the way, I'm thick-skinned: if this is all just too stupid to be worth answering then could someone tell me so?