I'm not positive, but I think you need the M8 bios, not the M8 Plus. I'm under the impression that the M8 is for 1.6 boxes, while M8 Plus is for 1.6b boxes. I have only done one mod on my own 1.6 and I used the M8. Someone please correct me if I'm wrong.
A little off topic, but I think Team Executer is supposed to be releasing a brand new 1.6 compatible X2 bios some time this weekend. You might want to wait for that one as a lot of people don't like the Evox bios, although I personally don't have a problem with it. But then again, I've nothing to compare it to.