1. Weigh or lightly spoon flours into dry measuring cups; level with a knife. Combine flours, flaxseed meal, and next 6 ingredients (through salt) in a large bowl; stir with a whisk. Combine buttermilk, melted butter, vanilla, and egg yolks; stir with a whisk. Add to flour mixture, stirring until smooth.
2. Beat egg whites with a mixer at high speed until soft peaks form. Fold egg whites into batter.
3. Coat a Belgian waffle iron with cooking spray; preheat. Spoon about 1/3 cup batter per 4-inch waffle onto hot waffle iron, spreading batter to edges. Cook 3 to 4 minutes or until steaming stops; repeat procedure with remaining batter. Serve with maple syrup.