Yeah, autoformer volume controls are indeed very high quality and don’t present the technical issues/considerations that smooth pots and stepped attenuators do. The thinness you’re hearing going amp direct could be due to several things, but likely is the most transparent way to go. As you prefer the sound with the preamp inline, I agree with what others have said. If you feel you’re getting the best sound with the amp’s volume control 3/4 of the way open, then roll with it. If it was a typical smooth pot, I’d say definitely turn it all the way up, so it is fully out of the way of the signal as much as possible. But since it is an autoformer, then this generally solid advice is not necessary valid in this case. I’m assuming your preamp has a smooth pot (maybe an ALPS?) in it, so in that case (if 7 o’clock is fully closed and 5 o’clock is fully open) then my advice earlier to adjust the volume control on your amp such that ~11 o’clock or ~12 o’clock + is the most used range on your preamp, still holds. The goal is to get the potentiometer in the preamp to not be used in that 7 o’clock to ~ 9 o’oclock range where they tend to have trouble with channel imbalances.
