Thanks everyone for your answers.
I'm having some problems with Nvidia Web Driver, so I want to go back to a "classical" configuration.
I tried to put the kexts into /System/Library/Extensions folder but there is no change. And when I put them in /Library/Extensions, my Hackintosh doesn't boot anymore, I've got a kernel panic at the begining (even without the dGPU). For both, I used KextBeast.
Into the BIOS, the two options that I have are :
Initial Display Output ==> IGFX (others options are PCIe 1 Slot & PCIe 2 Slot)
Internal Graphics ==> Enabled (other options are Auto or Disabled)