Dissolve instant coffee in hot water. Chill in refrigerator. Cut angel food cake into 1 cubes. Set aside. Combine mascarpone and cream cheese in mixing bowl. Beat until smooth. Add 2 tablespoons coffee, dark brown sugar, SPLENDA and vanilla. Mix well. Set aside. Pour cold coffee into shallow 9X13 inch pan. Quickly dip half of angel food cake pieces into coffee, and then place in medium glass serving bowl. Spread half of cheese mixture on top. Sprinkle with 1 tsp cocoa powder. Repeat with remaining angel food cake, cheese mixture, and cocoa. Cover and chill for three hours or overnight before serving. Note: Assemble tiramisu in pretty serving bowl or create individual desserts by assembling in large wine glasses. Variation: To make Berry Tiramisu add fresh raspberries or blueberries in between cake layer and cream cheese layer.