My Bangaii experiences:
I have kept (and bred) Bangaii for about 8 years. The are carnivores and I have never had problems getting any to take meaty frozen foods....Mysis, Brine shrimp, krill, plankton. They have not ever taken flake for me or other foods like squid, blood worms, etc.
One thing I have noted, they are very slow to eat and shy. If you keep them with fast, active or agressive fish like angels, tangs, or damsels, they will not feed. The other very active fish intimidate them and out compete them for food.
They do great in a passive reef system with fish like jawfish, gobies, firefish, blennies, etc.
I kept a trio in a 55 gallon set-up like this and 2 paired off and killed the third, giving me a paited pair. I read about breeding and put a long spined urchin in the tank. The male was not eating a week later and had a mouth full of eggs. About every 6 weeks I had baby Bangaii living in the spines of the urchin. Unfortunately most became fish food for the other fsh but I would usually get 3-6 grow large enough from each brood to swap at the local fish stores in Houston when I lived there.
I STRONGLY recommend you buy tank raised. They already eat prepard foods and the wild population is currently endangered.
I have considered selling my 125 reef and putting up anther Bangaii tank, I think a Red Sea Max 65 gallow would be perfect, and trying to breed them again. They are cool fish and do well in the right environment.