So guys, I finally found a way to make the GW card work on a N2DSXL!
First thing to notice is that you need a 3ds that already has an EmuNAND with GW compability. Without it, you can't setup GW on a N2DSXL. Personally, I used my old New 3DS XL (EmuNAND on 11.6).
For anyone interested, here is...