Synodontis are notorious for eating anything that will fit into their mouths, including tankmates, so food is not a problem; whatever you have onhand is probably suitable.
When the word "African cichid" is flung around, I am assuming that you're referring to tang/malawian/victy cichlids, which should not be kept alongside the mentioned species simply because their water requirements are so drastically different. As far as other riverine cichlids go (stenos, pelvichromis, hemis...etc), there are few cichlids too aggressive for these catfish. I have not had a problem raising some of the more aggressive ones (tilapia sp, specifically) alongside eups and angelicus synos.