its not so much the params of your tank, as it is the different attitudes. different fish put off different signs and signals. what could be a sign of being submissive and backing down from a sa/ca, they could interprit it as a sign of agression, and suddenly you got scales flying.
generally afro and SA temperments and behaviors dont get along at all... and its the afro's who like soft water as is. SA is hard...
if you really want to i'd watch carefully for awhile.
personally i wouldnt risk it...actually i probably would just to test it
Africans like hard water and SA like soft water. I have a tank with 4 - 12" adult Oscars in it as well as a 12"+ Royal clown and a 10"+ Marbled Bullhead. My Red Zebra and Maingano were to aggressive to stay in with other africans. My Maingano was killing everything even starting to pick on much larger haps so him and the Red Zebra reside with the Oscars and all is well now. The oscars looked at him as a snack at first but now they are all getting along. Go for it, it should work out fine.
Get your mbuna some rockwork to take cover in and live in and they should do ok. Everything about the different body language is true from what i have seen but mine still do fine. I have 2 12+ inch oscars in with a labeotropheus and some 1 inch fry and when the oscars go on the hunt the africans dive for cover in the rockwork. SO far i have not lost any. Mbuna like to live in rockwork anyway as they are cave dwelling. Here is a video and pics of my rockwork and fish so you can see an example of what i mean.
This pic here shows a simple easy cave i made out of a PVC elbow . I simply used GE II (use only GE II type silicone or fishtank silicone) i spread it all over the pvc elbow and then rolled it in dry sand from my tank. Let it cure or dry for two days then put it in the tank. The mbuna love it and you can partially bury it in the sand or gravel if you want to make it look natural.