My favorite amp continues to be my Dark Terror. Try changing all preamp valves to 5751's and you see how much more manageable the gain control can be.
I recently changed the PI valve to a balanced 5751, too. View attachment 11173
I'm guessing you prefer how the gain was changed by going to 5751s? Did you like the Dark Terror's gain structure before the swap? I have yet to roll tubes in my own DT as I have not fully explored what the stock tubes have to come offer me.