mbuna like the auratus are less aggressive when overcrowded. you could get several different species of mbuna and add it to the tank. if you go with several different species of mbuna, go for the more aggressive of them. would not put yellow labs in with them.
if going with the auratus, make sure that you get auratus. chippokae have the same female coloring as the auratus except that the auratus has a thin white line. chippokae is just yellow and black striped. same temperament though.
also with the mbuna try to pick out three females and one male. will also help out with the aggression.
mbuna means rockfish. add lots of rock for them to have places to hide and remember that they are diggers. if you add alot of rock, make sure it will not topple on them after digging. you can silicone a rock formation together using 100% silicone.