How to connect TL2000 with two SAS drives?

I have a Dell Powervault TL2000 with two SAS tape drives, a LTO 4 and a LTO 5. Both have 6GB SAS A and B ports. I also have a dual port PCI-E 6Gb SAS card in my server. Currently, the LTO 4 is configured as the 'control' drive and if I connect a single SAS cable from port A of the drive to my server, I can see the tape library (Medium Changer Device) and the LTO 4 drive - but how do you connect the second drive so it appears as a second drive in the tape library in Symantec Backup Exec? No matter how I try to connect the second drive, going from port B of the LTO 4 to port A on the LTO 5 - the server doesn't see the LTO 5 drive in device manager and neither does Symantec Backup Exec. What am I missing here? How do you use two tape drives in one library with Symantec Backup Exec? I can't find any diagrams or explanations on how to do it anywhere on the net and I can't be the only person on this planet running two drives in a tape library! Help!