Like most synos, pretty much anything goes, they are very adaptable omnivores. Try and give a good mix of meaty and veggie foodstuffs.
I'm about to order a bulk 1.8Kg New Era Plec Pellet tub for ~£45 (going to look at bulk Tropical/Catfish Pellets too), far more economical and I now know my fish love the New Era range after their Xmas present.
Another good bulk deal can be had on Tetra Prima, I bought a 3Kg tub for £70 delivered and I still have ~25% left almost 3 years on (I strictly only open tub briefly to refill my small containers for my 6-8 tanks).
They will love either defrosted or live bloodworm or alike as a weekly treat.
You could also mix things up a bit by offering floating food like Hikari Cichlid Gold baby pellets every now and again, allowing you to perhaps see your syno upside down eating from the water surface.