Sadly, it seems you're right mate. I have the exact same card and the bios isn't even flashable.
Here's what makes me think so, after issuing these 2 commands under pure DOS with a bootable USB key:
atiflash -unlockrom 0
--> OK
atiflash -f -p 0 modded.bin
--> ....
Programed = 0 Rom Size...