One more commentary from me, and I'll get off my soapbox.
When we think of a 300+ gal tank, in aquarium terms, it seems large.
But when comparing it to the river system istlantum dominates, and has pushed every other similarly competitive cichlid out of, that system is millions if not billions of gallons. A 300 gal aquarium is a puddle in comparison
Being aggressive may not be the only factor for its dominance, because it is an omnivore may have made it most adaptable and helped push others out.
But this is a similar scenario to beanii, it is also the sole cichlid of its habitat, and in most cases, trying to house more species in a tank with it, is also a bloodbath.
And look at haitiensus, there are no other endemic cichlids on the entire island.
In most cases if it can't kill other species housed with it, it tends to bloat and die of stress.
These natural indicators should be taken into consideration whenever trying to house any cichlids together.