I downgraded my AK2i (HWID 81) using this original firmware: https://filetrip.net/nds-downloads/flashcart-files/download-acekard-original-bootloader-1-0-f33562.html
In spite of the warning that "This won't work even on a CFW'd 3DS", it seems to boot both the kernel and games fine on my N3DSXL...
I like that games can be fixed after the fact, hate that it's being abused via beta tests... And DLC... I was a 7800 owner back in the day and loved Impossible Mission, turns out I couldn't beat it because it was actually impossible lol