Well I see you have already checked out planet catfish for info. Haven't found much other info besides them.
I didn't have a chaca chaca, but I did have a chaca bakaensis, pretty much the same thing. Mine would only eat feeder rosies. I was able to get him to eat a one cut up piece of smelt, but that was it.
I have heard them of takeing bloodworms, and blackworms. You will just have to give some stuff a try and see what he will eat.
They don't really do a whole lot as you have probably already relized, but they are fun to watch eat.
Oh, and they eat tankmates that will fit in their mouth.