Migrating from X-RAID2 single redundancy to Dual redundancy

Hi, I wondered if anyone might be able to help me in a similar situation please.

I have read different bits and pieces about dual redundancy : there is an option in front view to add it for new drives and that the option for DR is only available with a clean install,

I am using 4.2.25 on a Pioneer Pro, with five disks (2 1TB and 3 2TB). Most of the data has been pulled off it (only about 1.5 TB left on the system) as I'm assuming I have to rebuild the Raid. It's currently X-RAID2. I am using 4.2.25 as I have Mavericks and wanted to use Time Machine. I was hoping that when I added more disks there would be the option for dual redundancy in the Frontview panel, but it doesn't seem to be there under Raid Settings. Am I missing something, or was this feature perhaps removed from this RC1? In any event, any suggestions you can offer that might help me achieve dual redundancy without a rebuild would be most welcome!