Klipsch Speakers

Speakers aren't likely bright.  Your system is more likely bright. Speakers are reproducing what goes into them.   DaC?  Preamp? 

Some preamps or DACs have the ability to turn the voltage down, that will reduce brightness.

Some less expensive DACs sound great but they are bright.  My schiit BFII is that way (2nd system).

Jerry

Klipsch are forward lively sounding speakers.Forward lively sounding components driving them can be too much of a good thing.Sweeter more laid back dacs or pre amps are a good place to begin researching.

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.

No, use an equalizer to reduce treble.