Okay I got it now!!
Okay heres the deal, cichlids are incredibly territorial. I think you can probably house them both together, but it is how you introduce them that is going to be the roll of the dice. There are two thoughts... one would be to actually put the maingano in the 40 and the rest of the crew in the 75. You wait a couple weeks, and then you put the maingano in the 75 with the smaller fish that have been able to somewhat claim a territory. The maingano are then the new fish. This would be the safest route. The second is just add the smaller fish when you do a water change. When you add a bunch of fish it will shake up the tank and the maingano's and everyone else will have to claim a new territory. This is a little more risky, because the maingano's think the whole tank is theirs, but there is safety in numbers. So its your choice, but those are a few ideas to consider.
I am a little concerned that you have fish that are 2.5 inches and you think they are all sexed males? It is very difficult to sex fish at that size, so time will tell on that.