Thanks for the help guys! I uploaded the dru-842A firmware, it's version 1.60 - the only version from Sony so far AFAIK.
Liggy, when you say that the last 6 bytes tell you the drive type, do you mean it has the chipset info, or specifically that in this case it's an 842A? I took a peek at the firmware in a hex editor (I've done a little eprom hacking in my day), and I expected to see a text string there to ID the drive, but there wasn't one. It did look like a normal dump in that there was a bunch of code, then empty space and finally some data at the end (usually a checksum, is it in this case?).
BTW, if it'd help, I can grab a screenshot from Nero InfoTool so you can see what this drive/firmware claims it can do.