Heat large pot of salted water to boiling. Add pasta and cook until tender but still very firm. Drain thoroughly and transfer to mixing bowl.
Meanwhile, melt butter in heavy medium saucepan over medium-low heat. Add flour and stir until smooth. Reduce heat to low and cook, stirring constantly, 3 minutes. Gradually whisk in milk and broth. Heat, stirring constantly, until simmering. Stir in tomatoes, salt, and pepper. Simmer uncovered, stirring occasionally, 5 minutes. Remove from heat.
Add 1 cup Cheddar, the Gruyere, and Parmesan to sauce and stir to combine. Pour sauce over pasta and toss to combine. Transfer 2-1/2 quart casserole.
Bake 15 minutes. Stir carefully but thoroughly, then sprinkle with remaining Cheddar. Bake until bubbling hot and cheese is golden brown, about 15 minutes longer. Let stand 2-3 minutes before serving.