Place rhubarb, 1/2 cup sugar, and the water in a saucepan over medium heat. Bring to a boil; reduce heat to mediumlow; let simmer, stirring frequently, until rhubarb is very tender and beginning to fall apart, about 12 minutes. Remove from heat; transfer to a bowl; set aside.
Place strawberries in the bowl of a food processor; puree. Strain through a fine sieve or chinois into a bowl; set aside.
Scald cream and milk in a saucepan over medium heat. Do not let boil. Remove from heat, add remaining 6 tablespoons sugar, and stir until sugar is dissolved. Allow mixture to cool to room temperature.
In a medium bowl, combine cooked rhubarb, strawberry puree, cream mixture, and kirsch. Cover with plastic wrap, and chill at least 2 hours or overnight. Freeze in an ice-cream maker according to the manufacturer's instructions.