You can neutralize the preamp for practical purposes, by using the Tube Pre or a Clean Amp Model and keeping the preamp section as linear as possible...
a) Minimize the Gain and Input Trim.
b) Make that gain up with the Master Trim and Master Volume to taste.
c) Bias the preamp like the Tube Pre.
d) Use the Null Tonestack.
e) Turn off the Cathode Follower.
f) Turn off Preamp Sag.
...and finally, tune it how you like as needed with the power amp, power tube, and power supply params, plus the preamp biasing and preamp triode freqs (plate bypass caps). You can actually do a lot, and get perfectly workable power amp sims this way (grab params from your desired amp model).
Most guitar oriented rack mount tube power amps were just a gain/driver/buffer stage, followed by a PI and the power section, that's it, no tone shaping aside from the first stage's coupling caps and NFB (presence and depth etc). You can fake the first stage's coupling caps with the Amp Block's Input EQ's for some Mesa's that rolled off the low end quite a bit etc, and use the Presence and Depth controls. You also have the Output EQ's as well, and can place them anywhere you like, or use an EQ Block as well if you need more than 1 band of PEQ .
Good luck!
