Rinse the aronia berries and place in a container. Peel the orange and add the peel. Pour in both bottles of schnapps (1.5 liters total) and add the brown sugar. Stir well to combine. Let stand on a windowsill for at least 2 months, stirring daily for the first week, then every few days.
Add the cherry syrup and stir well. Strain the liqueur into bottles and cork them. Store the sealed bottles to allow further ripening.