Place a small mixing bowl in the freezer to chill for Step 5.
Puree raspberries in a food processor until smooth. Pass through a fine sieve set over a large bowl; discard seeds. Measure out 1 cup raspberry puree, whisk in confectioners' sugar (or Splenda), cover and set aside in the refrigerator for sauce.
Place orange juice in a small saucepan. Sprinkle in gelatin. Let soften for 1 minute. Place over low heat and stir until the gelatin has completely dissolved. Let stand for 5 minutes.
Meanwhile, beat reconstituted egg whites in a large mixing bowl with an electric mixer until soft peaks form. Gradually add sugar, beating until the meringue is stiff and glossy.
Beat cream in the chilled bowl until soft peaks form.
Add the melted gelatin to the remaining raspberry puree and whisk until blended. Set the bowl over a bowl of ice water and stir just until the mixture starts to thicken slightly, 5 to 10 minutes. Add one-fourth of the meringue to the raspberry puree and whisk until blended. Using a whisk, fold in the remaining meringue. With a rubber spatula, fold in the whipped cream. Scrape the mousse into a 6-cup metal bowl (or other decorative mold) or a 9-by-5-inch metal loaf pan. Cover with plastic wrap and foil and freeze until firm, at least 6 hours.
To serve, fill a bowl or basin (large enough to hold the mold comfortably) with very hot water. Run a knife around the edges of the mold. Quickly dip the mold in hot water, then invert a serving platter over the top. Grasping the mold and platter, jerk downward several times. If the mousse does not release, dip in hot water again and repeat. Cut the mousse into wedges or slices. Serve with the reserved raspberry sauce and garnish each serving with a scattering of berries and a mint sprig.