Flowerhorns or Midas would not have been my first suggestion. These guys can get really mean and with one bit can rip an African in half. If they are quick enough and smart enough and have enough hiding places then all could be well. There are several others that might do better. I know of someone who had an Oscar and a Jack Dempsey in a tank with some Mbuna and they all got along well for several years. But every fish and tank set-up is different. When you start mixing continents, all bets are off. I currently have a mostly African set-up (Vics & Malawi Haps) with some convicts, Gold Jack Dempsey's, Gold Severums, and a small Green Terror. They all get along fine for now, but I know it is possible that I could need to intervene at any time as this is a delicate balance. Also with a 75 gallon, you need to be careful not to overstock.
Have you thought about Red Empress or Red Fin Borleyi (Malawi Haps)? From your other fish selection it sounds like you are missing some red, and both of these fish get larger and have red/orange on them. Just a thought... You could get a smaller group and raise them up and sell off all but one male.