I think that the BIOS for the X3 is unique.
I'm pretty sure that it is the only BIOS that will run on the chip.
You can try it... flashing the wrong BIOS doesn't hurt anything.
Just set your jumpers to on on off off off which is the first bank in the chips memory and flash the X3 BIOS...
Then go to on off off off off which is the second bank. Flash the other BIOS and see what happenes... if it screws eveything up then simply go back to the first bank... (on on off off off)
There's no ill effects so just experiment.
I do think that the X3 BIOS is the only one that will work though...
Good Luck!