Ports 1-4 on your board are controlled by the nForce chipset, and 5-8 are controlled by the Sil 3114 chipset. You should be able to turn either chipset/controller on and off as well as set the mode they run at in your BIOS. Read you manual, or look a little deeper in your BIOS.
I use to have a UT series board from DFI, and I do remember these options are somewhere in that very, very, very extensive BIOS, I just don't remember exactly where.
On your board, which we do not know exactly which one you have buy the way, I am just going by the nForce UT board standards for a board with 8 SATA plugs, the Sil 3114 is an old SATA 1, or 150 controller.
The nForce SATA plugs are SATA 2, but it is also a fairly old chipset and actually performs on par or only slightly better than Sil 3114 chipset.