Firstly, I do not believe the memory which you are having has the XMP feature like this 4GB kit ("KHX1600C9D3X2K2/4GX"). But anyways coming to question as to how to enable the XMP feature here's the answer.
Please refer your motherboard's manual to enable the XMP feature. Click here for the manual!! Refer Chapter 2 - M.I.T (Page 35 - 45), this should guide you to enable the features.
One probability as to why the system is recognizing the memory speed as 1333Mhz instead of 1600Mhz is that the memory's SPD's (Serial presence detect) is programmed to JEDEC
standard latency DDR3-1333MHz though the memory is tested to run at 1600MHz. Hence, it is safe to run the memory at 1600MHz and you can refer the manual to set the frequency manually.