iyou can never have to much filtration, The xp4 is good by its self. But the emperors will help move the water and polish it they are mechanical and the Canister is for the biological.
Is this your first Tank
no it isnt. i have been keeping cichlids for over ten years now, but this is my first tank over 55 gallons. i have also never used a canister filter before. when i was setting my tank up i was told the two emporers would be plenty but after reading a lot of the posts on here i started to think otherwise