Personally I only feed my Kamfa Flowerhorn Grand Sumo Red, and Hikari Gold Cichlid pellets. IMO Grand Sumo is one of the top Flowerhorn foods out there, and have heard nothing but good reviews for it.
I feed him Grand Sumo regular/Red, NLS, Chingmix and freeze dried mealworm. Lately I've started giving him Hikari Massivore Delite and it's seem to be his favorite pellet right now.