Prepare drink mix according to package directions, sweetening with 6 packets Sweet ‘N Low®. Mix reserved syrup with enough water to equal 1 cup; heat to boiling. Meanwhile, in medium bowl, mix gelatin with remaining Sweet ‘N Low (2 packets); add hot liquid and stir until gelatin is completely dissolved. Stir in 2 cups prepared punch. In small bowl, with wire whisk or rotary beater, blend yogurt into half of gelatin mixture; chill both mixtures until consistency of unbeaten egg whites. Fold raspberries into plain gelatin mixture. In parfait glasses or dessert dishes, alternately layer raspberry and yogurt mixtures. Chill until set.