This could work. Gonna come down to the temperment of the Firemouth, but it's not like you have any real 'killers' there.
That's what I was thinking. I mean other than the firemouth, pretty much all of them are considered "peaceful" but some are "mildy aggressive" to conspecifics according the cichlid-forum.com. I will get the firemouth little, and if I see any aggression pop up I'll toss him a different tank. The Firemouth is the only slightly wild card. In fact most my stock list is currently in my LFS in a 55g and have all been there for about a year.