What oxford said is correct. There are 8 SATA ports on the Asus Rampage IV series motherboards.
4 SATA II ports connected to the Intel X79 PCH
2 SATA III ports connected to the Intel X79 PCH
2 SATA III ports connected to an ASMedia 1061 SATA III storage controller which is connected to the Intel X79 PCH via the provided PCIe lanes
The ASMedia 1061 is a huge piece of *** and should never be used except for eSATA. You can only use hard disks on this controller, no optical disks or SSDs. They will work, but they will cause a ton of problems including stomping the Intel storage controller's OPROM which will make the other drives unbootable. Additionally, the ASMedia 106x OPROM is not compatible with the EFI boot sequence, so booting from any device on this controller is a recipe for disaster.
I highly suggest that you completely forget that you have 4 SATA III ports and avoid using the bottom two. Just use the Intel PCH controller ports and the eSATA ports. If you need more storage space, get a proper storage controller.
EDIT: leave the Intel controller in RAID mode (this is AHCI firmware RAID) or AHCI mode and either disable the ASMedia OPROM or disable the device completely. If you want to use it for eSATA or extra hard disks, leave it in AHCI mode.