So all was ok i have successefuly downgrade my n3ds and i can use hbl with theme hax and my gateway card with no problem. After all that i have tried to update my emunand with xenon hack tutorial. I have tried different way with different update pack but nothing to do everytime my emunand brick and i have to reinject my emunand backup. I hope someone will find a solution, maybe when gateway give us support for emunand 9.6+. You are warned, when you downgrade you can loose the possibility to update your emunand.