You have to set the 5th multiplier bit to HI which will give your multi another x8, so if u set x5 it will actually be x13. Now there are many ways to do that, and I'm pretty sure you can find them all in the sticky at the top of the page.
I'll do a little searching and edit the post with links I find...
You have to cut the 5th L3 bridge to do that, here's the link to how to safely do this, better read the whole thread.