Hattor Audio Autoformer Reference Preamplifier

I believe Slagle at EM/IA (link), Nagy at icOn (link), Bent Audio AVC-1 (link), and now Arek Kallas at Hattor Audio (link) all use two AVCs for single ended preamps and four for their true balanced preamps.  The picture on the Hattor website link shows four and the verbiage in the Bent and icOn links discuss that four are required in their balanced versions.  As to why, I never questioned it but assumed each autoformer has an input and an associated output tap depending on the voltage reduction (i.e., volume setting), and that one AVC was required for each audio signal line so, one per channel single-ended and two per channel for balanced.  Whether it could be done differently I don't know, but they all seem to use two for single ended and four for balanced.  Maybe somebody who has built one can answer your question.

Having been both a happy customer of Arek's resistor based passive and a former AVC/TVC user, I look forward to your opinion on this new preamp. 

@mitch2 stated " the AVC sound was transparent, organic, and displayed a touch of warmth or body. "

This is not a criticism of the above description but a alternative description on how detecting such traits effected a different individual.

I agree there is Warmth or Body, In a variety of systems having heard a AVC / TVC in use, to my sensitivity and perception,  Warmth or Body, equated to a Weighty Underpinning of a Note > Vocal, to the the point it was a distraction for being the trait being noticeable.

For myself who has Transparent Devices, by Transparent I mean as good as invisible as a influence on a End Sound, Invisible to the Point, the Sources Effect on the Power Amp is all what is being produced as an End Sound.   

My experience of a AVC / TVC as a conventional place in a circuit as a VC does not leave me being able to suggest the encounter can be described as being  Transparent, the influence of the AVC / TVC on the End Sound produced is easy to be discerned.