the best dried food imo is hikari sinking carnivore pellets. they are on the expensive side though. especially if your cichlids chomp on them before they even hit the bottom of the tank. it is going to be tricky but one way that i have heard people try is the target feeding method. this would involve getting a long plastic cylinder (kind of like the gravel vacs) and placing it in the tank with one end if front of the bichir and the other above the water line so you can drop food in. the food will sink down the tube all the way to the bottom so the cichilds cant get it. once it gets to the bottom it is fair game though... good luck.
personally thats why i dont keep cichlids with bichirs.
edit: almost forgot to mention... the best diet for a bichir...i guess any fish for that matter is a varied diet. dont just feed them one thing. sinking carn pellets can be a good staple though. its nice to give them chopped shrimp, beef heart, smelt, etc. and i also give mine home grown feeders to chace around.