Found some info that might help
hereBasically, the SiI5723 Controller is a Hardware based RAID controller, so it won't really need any drivers in order to work. However, you should install the Speeding HDD app (or Silicon DriveXpert whatever it's called) to manage your array.
From what you've said so far, if you want to setup a storage mirror (raid-1) connect the two drives to the SiI5723 Controller (if you have data already on one, then make sure that's drive #1, and the other one should be blank, drive #2)
You can't use the two ports independently of each other, it's either you go RAID-0 (striping) or RAID-1 (mirroring)