OK here is my attempt at flushing out the whiteness or greyness as I prefer to call it. By having multiple materials employed you are going to introduce different shades / thinness/ colour added to the mix as well as different characteristic velocity properties. When a less good component or wire is introduced something is taken away in the overall result, e.g. all the notes are there but they appear washed out and not colourful and entertaining as a different combination; detail whilst it’s what we are all striving for is not the whole picture without vividness and a sense of being real.
It's most likely got more to do with the winding geometry and inter layer insulation material.
Check the pic, these traffos have more interleaved P/S windings than I have ever seen on an audio OP traffo.
WRT winding interleaving, the theory of some's good, more's better, too much = just enough doesn't necessarily hold.
There is an optimum number after which the whole thing starts to look more like a big capacitor (= simple explanation).
Do you know what he uses for inter layer insulation. This is very important.
My 2c worth - I used to work at a transformer manufacturer.
PS - I'll do a backflip if those conn wires are not silver
PSS - WRT quality of construction, they look bloody nice
T