mine eat anything i give them.. they have ate cichlid pellets, gold fish food, fish pond pellets. but mostly eat salad shrimp and the cichlid pellets, and minnows.
mine and others i know eat hikari gold pellets regularly. you have to put a whole bunch in at a time and then leave them alone for a couple minutes then one after another they pick them off. hikari gold floats though i don't know about the sinkers
mine dont hit the floating pellets that fast but they will eat with me in the room.. as long as im not right beside the tank. about 2-3 feet from tank at least. they are fun to watch when they eat floating pellets because they grab some food and shot down half of the tank..
Piranha are generally easy to feed but prefer meaty foods with ocasional live treats, crickets make great P snacks, If they don't like the dry pellets soak them for a few minutes in warm water and garlic juice to soften, then try it.