I would see if you can find some A. akindynos. They're a natural symbiot, and if you're lucky and can get the honey colored ones, that would look great against the red.
Another suggestion would be A. bicinctus. Although not a natural symbiot, I would think being in the clarkii complex it wouldn't be that much of a strectch for them to take to it. One thing to keep in mind IMO is to stay away from the CB, they look like crap. The WC are a nice bright yellow that would look great (assuming they would retain the yellow in the prescence of a host).
Plus, this complex can get large, my female akin is an easy 5", so they won't get lost in that huge tank.
Whatever route you take good luck. You may want to consider having another nem (or group of say, rbta) in the tank just in case some serious aggression breaks out and some clowns need a safe house.