Goto your device manager.
Look under your Universal Serial Bus Controllers group, does it look like windows sees the 3.0 controller? If so, right click it and click "update driver software".
Click "Browse my computer for driver software", then click "Let me pick from a list of device drivers on my computer", and then click "Have Disk..."
From here, browse to the extracted chipset driver exe file you downloaded, and then navigate to the following:
mb_driver_chipset-usb_fm2_w8\chipset-win8\Packages\Drivers\SBDrv\hseries\USB30\amdxhc\W764A\amdxhc.inf
Click OK, and it should say under Model "AMD USB 3.0 Host Controller".
Then click "Next".
See if that installs the correct 3.0 driver for you. If you get a message that tells you that driver was installed but the device is not active, then try the same as above except instead of "amdxhc", goto the "amdhub\W764A\amdhub30.inf" file.
Edit: Oh , and don't forget, when you're in the device manager list, to click the "view" toolbar and choose "show hidden devices".