I think I have seen almost everything there is to see when it comes to mixing lakes, and fish, and I have tried several not so smart things myself in years past. I have also seen odd mixes that worked, including a pair of Tropheus (Ilangi) that successfully bred in a Malawi tank, long term, with no serious issues. I have also seen a single Tropheus beat the tar out of every Malawi fish in the tank (including Mbuna), until it was later removed. Tropheus are typically extremely territorial, and sp. "black" are known to be some of the most aggressive of the bunch. A local breeder kept almost every species of Tropheus one could imagine, most WC, and I spent a lot of time in that fish room. I also grew out a group of red rainbows yrs ago, so I have more than just a little bit of exposure to Tropheus, and their behaviour. In the wild they live in the surf zone, with lots of water movement and high 02 levels. They are typically a very aggressive, very social fish that does well in large groups of their own kind.
Often times in this hobby it shouldn't be about what can I do, but what should I do.