OK
@SirKelly so let me get this straight:
1. You got a broken dev unit that you fixed
2. Found it had unknown tech demo on it
3. Tried to update the firmware and bricked it
4. Hardmod dumped the NAND and destroyed the dat0 pad on the board, but did get a NAND dump?
5. If so, what bootrom error is the 3DS now showing at boot?
Hate to break it to you, but if that's the course of events, you're pretty much fucked unless you can manually bridge the dat0 line and get console see the NAND again. Your only hope of getting into that NAND now is by doing that and using the (currently unreleased) ntrboothax to get the console running boot9strap and boot into GodMode9, on that specific 3DS board.
Another dev unit won't work, another retail unit won't work.
All 3DS units, dev and retail have console unique keys that would prevent that NAND from working on another unit.
That NAND backup you have is useless without knowing the console unique OTP and NAND CID.