I assume you have the Serial ATA version of the XRaid (the newer one) as the older PATA XRaid came with up 180 GB drives standard …
In this case, you can replace the drives in the drives modules and it should work out of the box, no updates should be needed. However, there are some compatibility issues with drives
that have ssc enabled, although the drives should now ship with ssc disabled by default.
In any case, there are
DOS utilities which allow you to toggle ssc on and off.
Just a note: like any vendor of RAIDs, Apple does not sell empty drive modules to customers.