Beat cake mix, water, oil and 3 eggs with mixer 2 minutes or until well blended; blend in sour cream. Pour over syrup in pan.
Beat cream cheese and sugar with mixer until blended. Add remaining eggs; mix well. Blend in milk and chocolate; gently spoon over cake batter. Cover with foil sprayed with cooking spray, sprayed side down.
Place tube pan in large pan. Add 2 inches water to larger pan. Bake 1 hour 30 minutes or until toothpick inserted near center comes out clean. Cool on wire rack. Refrigerate 2 hours. Invert cake onto plate; remove pan. Serve with cool whip. Makes 24 servings.