Some simple things I did with my Cornwalls - Punched out some .75 inch circles of black duct tape to adhere to the outside faces of the mid-range horn. Also, put one of the circles on the tweeter. This technique seems to be the perfect damping without over-damping, and you can play with it to your heart's content with a minimum of fuss.
Placed an 18 pound bar of lead with self-stick vinyl feet on the inside bottom of the cabinet (access via the middle front port) to dampen the cabinet low frequency resonances. More than this weight begins to over-dampen the upper frequencies.
Flanked the speakers with REL S812 subwoofers.
Did some work on the listening room.
Voila.

