Upgrading Audio Research Amps

What is the popular opinion on the sound of the new ARC models with the JFET input. I am not sure about upgrading a VT200. I like the all tube sound, but would like to hear opinions of people who have upgraded VT100, 200 or Ref 300
It is much improved. I heard the VT100 MKIII as well as the Ref300 MKII and the bass was better controled and the tonality was much better.
I'm more concerned with the change in timbre due to replacing the input tubes with JFETS