Connecting drives to a Smart Array Controller P840

Hello!
I need some help. 
I have a DL180 Gen 9 server. There are B140i (embedded storage controller) and P840 (external Smart array controller) in this server. There are three hot-plug drive boxes in this server. One box connected to the P840 controller with a SAS cable (connector from controller's side is wider than connector from drive cage's side).
Two other boxes connected to ports on the mainboard with two cables (connectors on this cables have same width on both sides).
I see through SSA that drives from the first box are connected to the P840 controller, and drives from other boxes are connected to the B140i controller.
How can I connect all my drives to the P840 controller? Should I have to buy a specific cable? Maybe I have to change something in settings and let the P840 controller "see" other drives.
I read a manual and can't find the answer to my question.