The cable plugs into the Expander and it takes care of the rest. That is how you get 24 drives. I will note that field changing of backplane configuration is not supported. It is selected at time of purchase. From what I can tell if you install a drive in slot 8 it should show up  (drive slots begin numbering at 0).
I have a PowerEdge R730xd with a PERC H730 Mini controller and want to know if I could add another H730 Mini. I'm wanting to provide room for an additional 7 drives and need to know if the chassis/mainboard can house both controllers.
Using multiple RAID controllers in a PowerEdge R730xd