Thank you very much for your time!
I didn't tried your method exactly, because i don't have an external HDD, but i used the kexts of your method. Now i made some progress and i am stuck in the "still waiting for root device".I tried with both IDE and AHCI settings (I have an MSI 790FX-GD70 motherboard) in BIOS.
Maybe it's the kernels i have used so far? What's the right kernel for the AMD Phenom II x4 965 Black Edition?
Thanks a lot!