Neither platties or fil barbs would work either with american cichlids. This is something I have researched and tried many different options. Here are a few fish that have the potential for working: Red tailed black shark, flag tail barb, possibly larger bala sharks, some puffer fish. Note that it depends on the size of the tank, hiding spots, size of the fish, what age they are put together.
Really, I have a school of 6 of them in with my AMERICAN cichlids. And I would not suggest ANY puffer as a dither fish.