Heat oven to 400°F. Spray 15x10x1-inch pan with cooking spray. In large bowl, stir muffin mixes, milk, butter and eggs just until moistened (batter will be lumpy). Spread batter in pan. Bake 10 to 12 minutes or until golden brown. Cool in pan 10 minutes. While still in pan, cut warm cornbread into 1/2-inch cubes. Fluff cubes. Bake 10 minutes. Stir cubes; bake 10 to 15 minutes longer or until golden brown on top.
Meanwhile, in 10-inch skillet, cook celery, onion, garlic and sausage over medium-high heat 7 to 10 minutes, stirring frequently, until sausage is until no longer pink; drain if desired. Stir pepper flakes and chile into sausage mixture.
In another large bowl, place cornbread cubes, sausage mixture and remaining ingredients. Stir gently, adding enough broth to moisten bread cubes but not make mixture mushy.
Spoon dressing into ungreased 13x9-inch (3-quart) glass baking dish. Cover with foil; bake 25 to 30 minutes or until hot in center.