My process was the same as yours, I burned the ISO and booted from it, I see the DOS instructions, but when I get to the part where I try to apply the firmware update, I get this error:
Model matched, no firmware match! Will not download firmware!
--
Model matched but firmware version is not compatible.
Hey! Yup we've exactly the same model type so there shouldn't be a problem, but you know, with what you described earlier trying it in a PC and the error message you're getting "model matched but firmware version not compatible" I got to thinking which disk image you're trying it off? Its not particularly clear on the site but there are two and for the mac (/or non PC intel&c.) there is a separate link to the disk image that I think has to be burnt- I've linked to it above but its on the site in the sentence
For non-Windows systems with Intel compatible processors we also offer a bootable CD ISO image, which will create a bootable CD.
my apologies if this is the one you're doing but its just what springs to mind right now...