Puree thawed berries in blender or processor. Strain through fine sieve set over bowl, pressing firmly on solids with back of spoon. Combine sugar and water in heavy medium saucepan. Stir over medium heat until sugar dissolves. Stir sugar syrup and 5 tablespoons cassis into berry puree. Chill berry mixture. Transfer berry mixture to ice cream maker and process according to manufacturers instructions. Transfer to covered container and freeze. Scoop sorbet into bowls. If desired, drizzle with more cassis and garnish with mint sprigs. dess 165