I have not kept BGK and Fire eel, but I would not mix fire mouth with G. balzanii.
I'm not worried about the BGK or Fire Eel... I've kept a fire eel before and I've have plenty of knifefish to practice on having a BGK.
And I have a firemouth male in the with my Balzini now and they get along great...And when I add the females his aggression will increase so I think they'll be fine.
yeah the FM pair might be a problem, the bgk should not cause any problems with that stock but they are easily injured since they are nakey, if you grow it out first until its larger before adding it then it might be ok, but i know i lost my first bgk to a pair of jewels i only had in the tank to make feeders but my bgk wandered over to their half of the tank one day and they completely shredded him down to the bone so i had to put him down
i dont know about fire eels
and you could do the larger peaceful cichlids like the chocolate or something, they prolly wouldnt have a problem, or severums would be good, in the bigger tank you really would have so many more options, a bocourti would also most likely not bother your balzanii and they are nice looking fish...
I said Chocolate earlier and someone said it would work... What about a school? instead of firemouth and chocolate?