Pit the cherries, reserving 18 cut in half for decorating the soup. You can pit cherries by cutting them along each side with a paring knife, but it's much more efficient to use a cherry pitter (they also work for olives).
In a mixing bowl, stir together the water and sugar until the sugar dissolves.
Puree the cherries in a food processor using some of the sugar/water mixture to get them moving or strain them through the fine disk of a food mill. Strain the pulp through a medium-mesh strainer.
Combine the sugar/water mixture, lemon juice, and kirsch, if you're using it, with the strained cherries. Taste the soup. If it's too tart, add 2 or 3 tablespoons sugar dissolved in 1/2 cup water. If it needs to be tangier, add more lemon juice.
Serve in chilled bowls. Decorate with the reserved cherry halves and serve with the cream.