The first two are easy: 1 - You may take some modeling clay and partially fill the upper lip in your horn. 2 - go buy a couple 2 pound "soft" weights made for diving (cloth bag filled with lead shot)and lay one in the top lip of each driver. Either of these will take out almost all the "ring" in you horns and tame some of the harshness you speak of.

This next option is a little more involved: You cut the welds out of the divider veins in the mouth of the horn, then fill it back in with some long life silicone glue like Permatex Blue gasket cement.

The last option is to dampen the outside of the bell with any number of sound dampening materials that add mass. You can buy spray on deadener like used in car audio applications, you can build up layers of latex paint and sand mixed together (layer it until the bell no loner rings when tapped with your knuckle), or line the lip of the bell with sound deadening rubber sheets.