While the tropheus get invertebrate protein in the wild from the aufwuchs, I wouldn't be feeding them straight protein sources at any point in the tank. A little too much and you might have a bloat issue to deal with, which really stings when it comes to more expensive fish.
I prefer to keep them in tropheus-only setups personally.
In the mixed tank, I'd stick to feeding things which toe-the-line a bit. New Life Spectrum is a good, quality food that would work well IMO. A quality spirulina flake would be another good base food for a feeding program in a mixed tank.