I have read that Duboisi do best in large groups, but your tank isn't large enough for that. Is that list in the first post all the fish/inverts you have in the tank? If so, do you know what kinds of "assorted africans" you have? You have some fish that will outgrow the tank (Frontosa, pleco) and some really aggressive fish (Duboisi, Bumblebee), so I really don't know that you should add anymore. Usually, its best that most Africans be kept in groups, but your tank just isn't big enough for that. The more aggressive fish are, the bigger the tank they should be kept in.
I think you should think about upgrading soon and then when you upgrade, think about adding more fish. You could possibly add something that is along the same aggression level as the fish you have, maybe a Kenyi, but I'm not sure how that would work.
Can you possibly post pictures of the "assorted africans", if you have some of these?