I'd also suggest you ditch the damsels lol. They are nasty little buggers and probably would be a nightmare for any fish you add. And when people get clowns they are usually quite small so that makes it even worse. lol
If you bring back the damsels you could start adding "happy" fish without worrying about aggression. I';d stay away from the maroon clowns though as they can be nasty as well. But a pair of oscellaris, mochas or even perculas would work fine in the cube. I had my b&w clowns in my cube for quite awhile along with a bunch of other nice fish and it worked really well.