Fragrant, ripe mangoes work best in this recipe. Check that the flesh yields to gentle pressure as a sign of ripeness.
Position oven rack to lowest setting, and remove the middle rack. Preheat oven to 425°.
To prepare the soufflés, lightly coat 8 (8-ounce) soufflé dishes with cooking spray. Sprinkle evenly with 2 tablespoons sugar. Set aside.
Place mango and nectar in a blender; process until smooth. Combine remaining 1/2 cup sugar, cornstarch, and salt in a medium saucepan over medium-high heat, stirring with a whisk. Add mango mixture to pan; stir until blended. Bring to a boil. Cook 1 minute or until mixture is thick and bubbly, stirring constantly; remove from heat. Stir in butter. Transfer mixture to a large bowl; cool to room temperature. Stir in egg yolks.
Place egg whites in a large mixing bowl; beat at high speed with a mixer until stiff peaks form (do not overbeat). Gently fold one-fourth of egg whites into mango mixture; gently fold in the remaining egg whites. Gently spoon mixture into prepared dishes; sprinkle tops evenly with macadamia nuts. Sharply tap dishes 2 or 3 times on counter to level. Place dishes on baking sheet; place baking sheet on the bottom rack of a 425° oven. Immediately reduce temperature to 350° (do not remove soufflés from oven). Bake 30 minutes or until a wooden pick inserted in the side of soufflé comes out clean.
To prepare sauce, combine sweetened condensed milk, juice, and water, stirring well with a whisk. Serve with soufflés.