Dewdrop is right - Maingano are hard to sex up front in the LFS. But you will know your boys from your girls when they are settled. The alpha male goes darker, and also while the boys are more interested in territories the girls seem to school together and wander around in a more relaxed manner - even with the other species.
Incidentally I love them and would recommend strongly a group of 4-6 for your tank.
For what its worth I also don't think your current guys are boring at all, and I really like Cy. Afra. It's on my list for my next new tank setup. I do agree though that you could easily double, maybe even triple, your overall stocking numbers.