^^ First of all, we hear things differently. My perception of too bright and rolled off treble may not be the same as your, so take it all with a grain of salt.
Tubes will flavor the sound based on their own characteristics. But in general tubes will give a warmer sound. Smooth treble and mids, and add a touch of bass. To my ears, tube and tube amps simply sound more musical and therefore more enjoyable. My experience is with the lyr and LD amps. I love the sound of vocals with tubes which is what I listen to most often.