This is sort of my point.You need less input signal to get the same SPL out of your speakers. The amps gain is fixed and it is only responding to what the preamp signal level output is.
If he is feeding it with a DAC then in almost every case I can imagine, the signal I’ll be cut in level going to the amp.
Having a lower gain preamp makes some sense, but the level of gain is unlikely to be creating distortion, unless the signal is being amplified first, and clipping or getting up there with respect to the rails.
I cannot picture an autoformer working too well near DC.The gain of the active tube stage in the Incito is fixed. The resistor ladder volume control comes before the tube stage and attenuates the incoming signal from the source. The gain adjustment of Incito is performed by changing the windings on the output transformers.
Passive preamps work only by attenuation of the output signal from the source before feeding it into the input of the amplifier. This can be done resistively or it can be done by switching windings on a multi-tap transformer or autoformer.
And we are back to low notes being removed with the passive subwoofer XO as being likely to help.Most active preamps work as a combination of attenuation followed by active gain. Only a very few have active gain adjustment where the gain of the active stage itself is adjusted rather than attenuation of the incoming signal. There are a few preamps that take the incoming signal directly into the active gain stage and then attenuate the output before sending it to the amp but this can be very problematic with overload if the output of the source is really high.
In the case of Incito, given the active stage is constant the distortion in high or low gain should be nearly the same...only whatever differences in distortion from the different amounts of transformer winding would possibly make them slightly different in that way.
That’s if that autoformer were being pushed to saturation near DC then it might affect other frequencies.
However there are so many moving parts here, that it seems like the game of tail on the donkey to attribute any specific thing to being what made it all sound good or it good.