My synos species like algae wafers. As the true upside down catfish tend to spend more time nearer the surface you might want to try them on something that doesn't sink too fast. Also try feeding after lights out as many catfish are predominantly nocturnal.
I don't personally keep any of those little guys but keep a great deal of the larger syno species. I know what mine like and that is the Hikari algae wafers, bloodworm, spirulina flake (yep they really do eat it) JMC catfish pellets and Hikari sinking wafers are very popular.
P.
Edit:I couldn't tell you if they'd eat the cherry shrimp or not. They may.....or may not. I've never seen my guys eat shrimp, although I do feed river shrimp to my Malawis on occassion (they live with my largest syno group).