atiwinflash says error reading rom.
It's more difficult to brick these cards than older cards because AMD's reference design has two copies of the firmware on them, typically a legacy PC BIOS firmware alone on one side of the switch, and then a hybrid that includes a UEFI firmware on the other side. Everything in this thread assumes you take the legacy firmware, add the Mac EBC firmware to it, and then flash it back. That means the stock hybrid side is still there ready to use and be able to boot the card.
So if you think you borked the firmware, flip the switch.
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the thing is BOTH are giving the same result
I just saw you did flip the switch.
This makes it feel like something's gone wrong with the hardware rather than bricking it from a bad flash, like accidental ESD frying a component somewhere. Or did you actually flash both sides? Are you positive it's fully powered/seated properly? When you tried to flash, does it give any more information at all?
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I'm assuming for some reason you flashed both sides of the card.
What does atiflash -ai 0 return? (or atiflash -ai 1 if it's a second card... same for commands below)
If that seems to "see" the card properly, try unlocking the firmware (atiflash -unlockrom 0) and forcing a flash (atiflash -f -p 0 yourfirmware.rom).
If it doesn't "see" the card properly, then I suspect the hardware is damaged.