Tube Pre uses the Vintage tonestack which is flat when the tone controls are at noon. source
It may not be perfect compared to products specifically designed to support what the OP is trying to do but it is cartainly your best option with the Axe. You have filters, many types of EQ, and ears to compensate for anything in the frequency response that is non-flat. While I got rid of my tube preamps when I went Fractal, I would not hesitate to use the Axe as a power amp sim using the tube pre a cab block and a parametric EQ block or two, if I had this need and I'm confident it could yield excellent results even if it is not a turn key solution.Not my experience Yek as any passive tonestack is anything but flat at all settings?
I would've loved for the Axe to be able to do it but if you compare the Axe with the vintage tonestack to say the Two Notes Torpedo's or Peavey's ReValver's tube power amp sims you'll hear a huge difference (remembering that tube power amps do not have tonestacks etc).