Soften gelatin in water; set aside. Combine sugar and juices in a medium saucepan, stirring well. Bring to a boil; reduce heat and simmer, uncovered, 5 minutes. Add softened gelatin, stirring well. Chill until the consistency of unbeaten egg whites.
Slice angel food cake into 1/2- inch - thick slices. Line bottom and sides of a 9-inch loaf pan with cake slices, reserving any remaining cake slices.
Add orange sections and marshmallows to chilled orange juice mixture. Gently fold in 1 cup whipped cream. Spoon mixture into prepared loaf pan, and top with remaining cake slices. Cover and chill overnight.
Unmold cake onto a chilled serving platter. Garnish with sweetened whipped cream and orange slices.