I would assume that you would need to reformat the current drives. I have not herd anything on the other forum post where you could run multiple drive styles at the same time(Raid 1 +Raid 5). Those you could easily just remove the current drive and place the new blank one into the system and then format it to the desired style and insert the other drive with the different style format.
Im using jbod today and have one disk. I want to add three more and un raid 5 instead. Do I need to format the first disk so it fits the raid 5 or can I keep the data on the disk and its converted to raid 5?