yeah well those links that were posted seem to suggest that it is possible to add a drive, but it wouldn't let me add a 3rd to 2 in raid. Have a look at them, they might help.
I won't raid till i get the new boards here, which could be a while after I contacted the seller.
I ended up leaving the OS and programs on the raid0 setup, and keeping the data on a 1TB. The setup looks extremely ugly, with hardly any of 2TB used, while all my data is hogging most of the 1TB, but at least it (and I) are safe