Unless you get a mean male or two females that hate each other, the three frontosa should work in that tank-- how you arrange the tank may also be a factor. I was a mod for years on cyphos.com and most people found Placidochromis phenochilus to be compatible with Cyphotilapia in 6ft tanks, whether 5ft is enough for 3 and 3 I'm not sure, might depend on the individual fish.
Based on my experience, I wouldn't do A. baenschi with them, I'd reserve them for an all Malawi tank. Mine were among the more aggressive peacocks I had and, for one thing, fronts are happier without a lot of craziness in a tank and, for another, I wouldn't want the fin nipping-- I get the idea of adding a complementary color, some people tried it with yellow labs (L. caeruleus), but often as not they were too nippy. At various times I did do Mdoka flametail peacocks and Otopharynx lithobates "Zimbabwe rocks" and, at least for me, both worked well (with C. gibberosa "kapampa") in a 6 ft tank. I saw a couple of other guys do the Mdoka flametails with moba and it worked for them also.
I understand sticking to a Tanganyika only approach, I did that also sometimes, and sometimes it was Cyphotilapia only, but you can mix some Tanganyika and Malawi cichlids if you get the right species.
