By double downhaul do you mean the down haul is attached to both sides of the sail or two points on the same side? If so where are those points.
There is a cringle in the centre closer to the luff with a loop on the other side of the sail closer to the leech. The downhaul is passed up through the chute, through the cringle and attaches to the loop; this effectively doubles the sail when hauled, bringing it down folded. It recovers to either side, depending on where the downhaul is reeved.
I would be interested to know who made the assymetric for you.
Neil Thornton of No 1 Sails of Middlestown, sadly now defunct as Neil is now making Micro Caravans somewhere in North Yorkshire!