It will not work properly without this cable attached. There are two USB ports on the outside and a connector that can be split into another two so you could replace the USB ports on the front with USB 3.0 ports if you're adventurous. I haven't checked out how hard that would be yet.
[ edit: You also must remove PXHCD and/or any other kind of driver hacked or not so that the Apple driver takes control ]
[ Update: User
has verified this also works for the ExpressCard version of this card for laptops, just forget about the power cord part]
Here is the link: