I'll first need someone to confirm that we have everything we need (besides the OTP). Although to be fair, we technically already updated to 6.x and used it as the base to downgrade.... Either we have everything we need already or it was lost the moment we updated to 6.x... Right?
You've got an actual full NAND dump now, also the XORpads. This is more than the regular a9lh installing user has, and means anything that comes up will be 100% fixable at least with a hardmod.I'm tagging @d0k3 for him to check, but you may have a point.
Now, D9 worked via mset? You can get FBI on there (safeSysUpdater, too) via the injector, and maybe get rxTools to run it. From there it should be easy. Always be careful, and maybe ask someone who knows better (I don't know much about how the updater works).