(slightly modified from Sangria: Fun and Festive Recipes)
In a large (at least 2-quart) glass pitcher, combine the lemon and peach slices. In a separate glass bowl combine the lemon juice, Licor 43, and sugar, and stir until the sugar is dissolved, then add to the peaches and lemons. Slowly pour in the wine, stirring gently. Refrigerate for at least 2 hours or as long as overnight.
When ready to serve, add the plain seltzer and stir gently with a long-handled wooden spoon. Pour the sangria into large glasses, allowing the fruit slices to fall in. Fill the glasses with the ice cubes first, if your guests desire ice. Mine have tended to refuse the ice, since the sangria is already chilled, and the melting cubes just dilute the drink.