DL580 G5 Add drive cage

[G-MAN]

I advice I need to add the second drive cage option to a DL580 G5. This requires another Raid controller would it be best to get the SA P400 and connect the two drive cages to this on it's two internal ports and disable tho onboard P400i controller. What do you think the best option is for adding the second drive cage with controller?

[JKytsi]

Choices are
400i to first cage and P400 for the another
or
P400 for both

[G-MAN]

So one P400 should support both drive cages?
I am looking on keeping the existing array config and expanding the array. Can this be done if I replace the P400i with one P400. I realize it has two internal ports but the cabling guide I am looking at shows both ports going to one drive cage and the same for the internal P400i?