The solution is to cripple the drives to 150MB/s with a jumper and then these larger SATA2 drives will work with Apple’s RAID Card.
This can be done by jumping the 5 and 6 pin on the Western Digital’s and the 1st and second pin on the Seagate’s.
Just google Seagate or Western Digital 150MB/s jumper.
worked for me.
So, now I have RAID 5 with nearly 4TB worth of space.
Good Luck!