On controller 2:
Create a new aggregate of 13 600GB disks, and keep one as hot spare.
Copy the root volume from the small SAS aggregate to the newly created FC aggregate.
Assign the SAS disks on controller 2 to unowned.
On controller 1:
Assign the old Controller 2 SAS disks.
Add the SAS disks to the SAS aggregate.
Reallocate the volumes (if there are any besides the root vol).
No need for maintenance mode to do this.