They've actually been filling up on the ray's worms lately. 3/4 usually eat smelt, the one that doesn't only eats worms since that tank doesn't get feeders anymore.
One things sure though, they know better then to try to beat out the Armatus for smelt. Maybe that's why they have been eating worms, they don't have to swim for thier lives afterwards since these Armatus seem to ignore them.
This last batch was broke with a fishing string and cut smelt. There's easier ways if your tank allows, mine has too much current for Krill. Check the "Payara Captive Care Guide" stickied in the "Other Characins" section of the forum, that might give you some ideas.