Buttekoferi has been sucessfully spawned in aquariums for many years. The information in the Baenschi Atlas is often old or not accurate. Variety in diet is always good, and providing different foods insures that your fish will be in good condiiton and more readily spawn. In addition to being snail eating experts, they also eat vegetable matter like plants, and algae. Providing foods high in vegetable matter is as essential as providing snails. I would say you are doing fine in the diet department, and would add more veggies to their diet, rather than protein.
Although they will eat smaller fishes if added to the aquarium, I would not feed that type of foods to them, I think it is just too rich. It is important not to over feed your fish as this will cause problems too. Obese fish are not as likely to reproduce, and in our aquarium fish just don't get the excercise like they do in the wild foraging for foods all day. Many therorize that keeping your fish on the hungry side increases their need to reproduce, to keep the species going. Buttekoferi has a reputation of being one of the meanest cichlids around, and often will kill off tank mates with no remorse. Feeding them smaller fish seems to make them even more aggressive.
They are sexually mature long before they reach their maximum size, and spawns easily number over 1000 fry each time. Manipulating their temperature can help induce spawning. Keeping them at temperatures around 76 - 78 degrees F., performing a major water change and increasing the temperature up to 80 degrees F. may encourage spawning.
They are good parents up to a certain point, usually when they are ready to spawn again, if you don't remove the fry, they will eat or kill them. It is best to remove the spawn to a grow out tank soon after they begin freeswimming and then feed them freshly hatched baby brine shrimp and after a few weeks they are able to take finely ground dry foods also.
Buttekoferi is not very popular among hobbyists since the spawns are so large, and they are so mean. They will not tolerate tankmates, so they end up taking up a whole tank on their own. However it is still a fun fish to work with, and watching the spawning ritual and parental care is always rewarding. It is a cichlid you want to spawn for the challenge, as there is no monetary value of their fry.