You can often flash these raid cards into IT mode to disable raid and so that they just pass through the raw disks. That way you can hook up either SAS or SATA drives and run them with software raid of your choosing, like ZFS. SATA is probably the safer bet since you will be able to use them in a future build without issues, but there’s no issue with SAS.
If you can’t flash this raid card to IT mode you can buy a cheap LSI 92xx card. They are quite common and cheap, and easy to flash to IT mode.
With a SAS card in IT mode it will show up in your OS as 4 different drives. You can mix and match them however you like. You aren’t restricted into pairs of 4. In fact one SAS cable can be multiplexed into many more than 4 drives.