My current all male setup is giving me no problems at all. All of my colors are great and developing. I'm also having great luck with the placidochromis(I have 3 species) and copadichromis (2 species). I currently have them housed with 4 species of peacock. Check my signature.
Holyfish has some great suggestions! that Ivoryhead won't do well if there is too much agression. Watch out with the placidochromis, Milomos are mean and big, and Phennochilus are a favorite but can get big as well.
As I said, I like Holyfish's suggestions... maybe do a Red Empress or Phennochilus or both.. maybe a Stuartgranti Peacock like a Ngara or Blue Neon... a A. Koenings/Mbenji might work out. I think every tank needs a good Rubescent peacock. Midnight peacocks are cool and stay small... Don't overcrowd, you can overstock, but overcrowding doesn't make that nice of a tank and can easily be done in a 75g!