I'm the living testimonial and last survivor for this bricking journey. I had my device rooted on the second day that I got my KFHD, then bricked it and kept in the kindle fire bootloop for days.
I was a bit sceptical to buy a factory cable initially as I would have to wait for weeks over this part on earth. But after reading all the sources available online and I know this factory cable is unavoidable, I ordered, waited and received my factory cable and guess what, this is just like the immediate antidote given to the sleeping beauty, after I plugged in the factory cable and carefully followed the instructions by the seniors here, I unbricked my KFHD in 10 minutes.
My two-cents advice is, if you are adventurous type and plan to go wild with your KFHD, get your factory cable before anything else, then, you can experiment all the wonderful ideas/ modding here.
Good luck and have fun!
Sent from my KFTT using xda premium