Put the simple syrup and mint leaves in a pitcher and muddle with a wooden spoon. Fill the pitcher with ice, then add the amaro, rum, sweet vermouth, lemon juice and orange juice. Pour into a tumbler filled with ice. Top with club soda and garnish with mint sprigs and the orange wedge.
Use 3/4 cup simple syrup if you prefer a sweeter drink or less if a tart drink is preferred.