Well I kept my duboisi with mbuna and they did just fine for the couple years I kept them. I think the calvus will be much intimidated and never come out and possibly starve to death.
You may find with only 5 africans in that tank that fighting becomes a problem, and duboisi are no slouch at that. You will also need to stay on top of water quality.
Well they have a reputation for being difficult to keep alive. They're certainly not a beginner fish, or one for the person who doesn't like water changes
dont know about the duboisi, but i think that the calvus would be to weak to compete against mbuna, sure calvus are pretty hard-core fish in their own right, just not as hard as mbuna
I wouldn't get either. Unless you have the space...T. duboisi do alot better in groups of their own species. I'm not too sure about how aggression pans out amongst them but you're lucky that mbuna and Tropheus have the same food requirements if you really decide to go for Tropheus.
I tihnk a single would be fine. I would again note that Duboisi are very sensitive to shabby water changes, including presence nitrate. I would be looking to change my water at least twice a week, no matter what you're doing with filtration.
For the record my Alto Comp is fine with my Mbuna and Haps. No one bothers him, he doesn't bother anyone. Him and an Afra have taken up a hole in the rocks together acctually. The afra nudges to Alto Comp but he does his little body curl and it all stops. Alto Comps are similar to calvus so...just throwing my experiences out. Oh and mine is fast to the food. I did have 3 Black Calvus as well doing fine until the heater killed them.
I guess it just depends on the type of mbuna you get or the certain personality of the fish.