Ur current RAM don't support 1600 as default or as an options in the BIOS, in this case u need set all the specifications of ur RAM manually in the BIOS.
How do u do that? U need enter to the BIOS of ur mobo (I think that ur BIOS mobo is something like this
), look for the option advance memory settings
and I think that u can find there the options to set the specifications of ur RAM manually.
U only need change this: CL, Trcd, Trp, Tras and also set the voltage to the specific of ur RAM.