No way to adjust memory speed in BIOS

Hey guys I have a ASUS CM6850 (well basically just the motherboard and processor from one.). I have upgraded the case, cooling, memory, and video card. The basic problem I am having is when I enter my BIOS to enable the XMP setting for my memory I have no AI Tweaking option under my advanced options tab. The computer came from factory with 2gbs of 1333mhz memory, I have upgraded to 8gbs of 1600mhz and have no idea how to make the memory run at 1600 instead of 1333. I know I should just be able to enable the XMP option in my BIOS but like I stated earlier I see no option for that in my BIOS settings. Is there any other way to make this memory run at 1600 or am I just stuck with it running at 1333?

If PC wasn't designed to work with higher memory frequency and there is no option in BIOS to change it then you won't be able to set higher clock. I guess it wasn't planned to be released with faster memory. The same is with many other branded PC.
You can change memory SPD profile so it boot at 1600 without XMP profile but for that you have to edit memory SPD profile. To do that you need something like Thaiphoon Burner software. However it's not guaranteed you will make it work and at least in this case I'm not sure if it's worth it as perfrmance difference won't be high.

Ok thats what I was thinking as well thank you for your help. Just time to invest in a new motherboard.

I would already move to new platform if you have to spend money on a new motherboard.