Thats a very nice fish you have there. I have a 10" sohal myself. Awesome fish. I have had him and a Naso for about a month now. I bought them off another person who was selling everytihng. the Naso is 8" and loves the Pace. I have mine in a 180 with an onyx clown, a pink spotteed goby and a newly added bi-color angel (centropyge). the clown and goby were already in the tank. it will be a full blown reef once I get over a little bout of Crypt on the sohal.
while I have seen the sohal bully the goby, i have never seen any agression on the clown, and when I added the bi-color, the sohal took one look and went about his business. as if not to care about the new little 2" fish. from what I have read, you can add fish that have no intimidation factor for the sohal and they will usually accept them without any agression. I am going to hope this is true and give it a try for my fish. I have also seen some with a cage built that allows a new fish to be acclimated with existing fish that would otherwise fight. I have a guy who has been very successful introducing several angels both dwarf and large into an existing tank together. a week or so in the box and the existing fish is used to the new fish.
In my tank now, the naso is the hyper one. constantly tring to make waves on teh surface,while the sohal blissfully nips at the rocks and glides thru the holes.
with the smaller reef fishes, the more they can hide, the better they will be. If I were you, I would increase the ammt of rock in that tank to about 400lbs or so giving you plenty of reef structure for the little guys to hide in. you may be very surprised.
Here are my babies. that poor clown sometimes gets run over at feeding time as they can sometimes get a bit out of control and will run into the clown. the clown will also get up there and eat on the nori with the two pigs.