I like the Rams idea! But what about the higher temps needed for them will the acara be ok?It could be done, but personally I would stick with south American cichlids. The firemouths are centrals and while not the most aggressive CA cichlids, they can get a bit more aggressive than the acara, and like to be in groups of 5+. Also, while both fish are adaptable, the firemouths prefer hard water and higher pH, while acaras usually like softer/lower. Some other good suggestions would be:
festivums
guianacara gaeyi
keyhole cichlids
bolivian rams