your reference model will not flash to a devil 13. totally different PCB. But yes, if you were to flash your bios on your card, you would need to flash both master, and slave. The Command would look something like
Atiflash -f -p 0 masterbios.rom
Atiflash -f -p 1 Slavebios.rom
Where on MY card 0 is the location of the master bios, and 1 is the location of the slave bios. make dually sure this is the case with your card as well. Atiflash -i will give you adapter information.
with the bios switch on one setting, so make sure you dont have that switch on the read only settings.