Configure more than two logical drives in an HP ProLiant Gen8 server?

I've a server HP Proliant dl380 gen 8. I've got 2 RAID 1 drives (each having 2 HDDs (300gb) in a mirror). I've now come to put 4 extra physical disks into the server and it won't let me create the logical disks for the 2 new drives. I want to create an other new logical drive for thoses 4 physical drives

When I try to add them from the RAID utility (F8 during boot) I get a message saying ORCA can't handle any more logical drives, and that I should use the array config utility to add them. I tried using the array config to add them but can't see how to do it. The disks are both picked up and labeled "un-allocated" but I can't find any way to allocate them.