Question about my RAM

Hi,
I recently got two Kingston HyperX 1600mhz RAM sticks. Under my system they are running at 1066 MHz. I want to change them up to 1600 MHz but CPU-Z reports the max bandwidth as 1333MHz, even though they're 1600MHz sticks.
Can someone explain why it claims they're maxxed out at 1333MHz. Thanks.
Also my system is N68-VS3 FX motherboard, 8 GB of Kingston HyperX dual channel memory, 400w CoolerMaster PSU, AMD Athlon II x2 270 CPU, and currently onboard graphics.

Thanks,
Samuel.