ok I get the point: NAND mode does not mean that I'm installing to sysnand and SD mode does not mean that I'm installing to Emunand.
So I guess that I'll have to go boot on sysnand and install TWLFirm_N3DS.cia there.
So I guess that I'll have to go boot on sysnand and install TWLFirm_N3DS.cia there.