Well, after spending numerous hours disassembling the bios update, I know how the update executable works probably better than anyone other than the original engineer who wrote it.
It's a modular program. Clearly designed to work with multiple PCs, though only the XPS portion is compiled into it.
It installs a kernel-level driver service. Which is activated by sending a specific windows message to the service.
It checks a bunch of bios settings to make sure you're on a Dell PC. Then it looks at your specific device model # and revision #.
If you're on a Dell, it's pretty trivial to hack (jnz -> jz, twice) to make it work.
That said, I'm done. The patched (cracked?) exe I have should run on a 9300 and update the BIOS. Several other things will really need to be done to run the 6800 Ultra on the 9300, though:
1) Power. Needs more power. Spare parts might have the XPS 2 power supply and it might be replaceable. Will also require a XPS 2 power brick. Yarg.
2) Bios checks removed for the battery. Cuz I'm not upgrading to a 9 cell battery.
3) figuring out how to underclock the 6800 Ultra would be the safest bet. I wouldn't run it at stock until you see how well it handles running on the 9300 heat layout
All in all, this upgrade's pretty silly. I'm just mostly interested in it not to save money, but to be able to upgrade to a better video adapter later down the line when I have more money, since I blew it all on the 9300