This is only true for 1.6b's ..... if you flash over the 3.0..3 FLASH BIOS - nothing else will work as generally the backup BIOS is 3.0.0 and 3.0.3 is only normally flashed to ONE bank on a new X3.
A 1.6 ver tho, will boot to either 3.0.0 or 3.0.1 I THINK - both of which are normally on there, certainly the backup.
However, there have been a lot cases of people having trouble flashing - overflash the 3.0.3 and then having no-where to go, as it were. You either then have the choice of sending it back to the supplier to re-flash, or get a third party (like myself) to do it for you.
The answer for 1.6B owners? Once you find the 3.0.3 FLASH BIOS, which is normally on bank 2 (off,on,off,off) - MOVE THE SWITCHES BEFORE FLASHING !!!!! Put them back to the on,on,off,off config, thus leaving bank 2 and the 3.0.3 intact for future upgrades.
Once the 1959 BIOS is working , you can (again as I have done) upgrade the backup FLASH bios to 3.0.3 to save yourself future embarassment. Obviously you could just upgrade to the 2666 BIOS or whatver, through the exisitng 1959 but I like to have a saftey net - in this case the backup FLASH bios.....
Stay safe kids !
J