I set up one of my 8 slots to have "No Amp Model".
I selected the settings I wanted pentode, class A/B, even gave it a cabinet choice to get that EQ flavor assigned to it...etc.
But now, when I choose that slot I have a great tube power section with a relatively uncolored front end for using what ever preamp I want.
Right now the Kingsley Jester and the Xotic SL Drive are taking turns being the preamp for that slot. And they are both doing really well at completing the package!
It's like finding yet another useful blade in the old swiss army knife.