Try Nordost speaker cables. Even better, replace the passive with an active x-over and use Nordost cables.. It will change everything.
My personal experience with KHorns is limited to the La Scala but from forum exchanges I know that Klipsch speakers have in general certain problems like too bright etc.
Good tube amps with linear frequency response will not change the sound of these speakers. However, you can adjust the brightness and other nasty things with a good parametric EQ if you know how to use it. Probably the cheapest and easiest solution.