I don't see why you can't put another clown species in your tank, especially being that it's so big. I agree that clarikiis are aggressive though, so I wouldn't go with them particularly.
In the beginning stages of my tank, I had a small oscillaris and a small maroon clown in the tank together, and they weren't aggressive toward each other. In fact, whenever my evil blue damsel would try to nip at the oscillaris, the maroon would defend him and chase the damsel away.
My friend has a 55 with a pair of black sebaes, and he kept a pair of perculas in there with the sebaes for a while. The perculas got ich and died, but until they died they never fought.
Definitely wait it out too though, like everyone's saying, it can take some time for the symbiotic relationship to develop. But as far as more clowns, as long as you choose carefully and try to make sure they're all around the same size, I don't think it'll hurt. JMO.