Yellow labs are a nice choice, but I'd steer clear of demasoni since they're pretty nasty temper wise. You'd need a bigger tank (55G+) with multiple Demasoni to spread that aggression, or multiple species of males. Shell dwellers are also a good choice for a 28G, though I'm sure someone with Tanganyikan experience can chime in with suggestions. I actually had 6x Ps. Saulosi in a 29G, went well but they weren't fully matured or had females, so the aggression wasn't that bad yet. Honestly for this size of a tank, I'd only go with 1 specie and have dimorphic breed like, Saulosi, with a 1:4 or 3:9 male to female ratio (though 3:9 is REALLY pushing it). This way aggression isn't too bad, you get popping colors, and little juvs swimming about in the future

just my 2 cents at least lol