Also a Synodonis catfish works well with Africans. I have one and a patriot crab in my tank. The crab is a sideways walking garbage compactor.
As far as I can see in your pics you appear to have a Kenyi, an Auratus and an Acei. You could add several more to your 55 to spread the aggression throughout the crowd. And just for the fun of having more fish. There is an awesome site called Cichlid Recipe that might be helpful.
Congrats on a nice looking tank with some purdy fishies.