From my, admitedly limited, experience of modern SS amplifiers with Valve Pre-amps, the valve pre-amp has negligible effect on the tone. I currently have a Carvin BX something or other, but to be honest I can't tell the difference between the Valve in or by-passed. I've also read comments here and elsewhere about the Markbass Valve premps being "Very subtle". I'm comparing here with the wonderfull Marshall DBS system, or even their B150 Combo; both of these have blendable valve pre-amps that really make a difference, to the extent that it is actually useful to be able to blend between the two.
Are there any modern SS amps out there where the Valve Preamp has a noticable/useful effect?