Tube sound: Pre-amp vs. amp?

You do not say what your source is! Assuming it's CD, might it be your CD player adding the HF edge? Regardless, a tube preamp will reduce the HF edge, but it will not remove the transistors from your SS amp. Transistors have their own sound as well. In short, yes, a tube preamp will warm your system. Be sure to try your choices in your own system to be sure you get the sound you seek.

Depending on how high end your CD Player is you may try an inexpensive tube buffer stage in between you player and amplifier. Musical Fidelity makes one for $200.00 (much less used) that does this trick but may slow the tempo somewhat per recent reviews and feedback. I assume that there must be other models that are also low cost. Maybe someone at this sight knows of them. The con is that you will need another pair of interconnects to hook it up.