Hm.. I'm interested in this too. I'm thinking of adopting a Blue crowned and introduce him/her to Mango. I'm not very informed on it, but what I have been told is the more gradual, the better. The biggest thing is about a month or so of isolation, kept in separate parts of the houses, and they learn to get to know each other through scent's, and it helps stop the spread of disease. Then you put the cages in the same room during the day for a couple of days, then 24/hours in the same room, then letting them out of their cages together and then eventually setting both of them in a large, neutral (no territorial issues) area of the house (like the kitchen or something) and then supervise them closely. You should be able to pick up aggression immediately too if you know your birds! The key I suppose is to just go slowly.