The key here is booting into DOS and typing command once in AtiFlash folder, "atiflash -i".
If you see your GPU, you are golden!
Otherwise, here is my opinion, I think the best way is to have a GPU with a different interface, either PCI or onboard. Or if you mobo BIOS has an option to disable Crossfire, then that option of having a second PCI-E card in the primary slot is viable. It worked without a hitch is because I had a completely different interface GPU as secondary.
Also, if you notice, the TechPowerUp guide also mentions to put in a "PCI", not "PCI-E" as a temp card to unbrick your primary card....I believe this is the problem!