Effect of Speltz Autoformers on Sound Quality

I would appreciate anyone's experience with the Speltz autoformers.  While the autoformers do increase the impedance the amplifier sees, it would seem that the long length of wire in the autoformers will affect sound quality.  Has anyone compared the sound quality with and without the autoformers in their system using an amp which will not be negatively affected by a low impedance speaker?
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I used Speltz autoformers for a while after I got Atma-Sphere MA-1 amps. With 8 ohm speakers (Abrahamsen, Aurum Cantus). I felt it introduced a slight veiling of the sound. I was much happier after I bought 16 ohm speakers (Audiokinesis Dream Makers). Even if the autoformers are good (they don't do much harm), I think that in order to get the best sound from OTL amps, matching speakers is the way to go.
Thank you for sharing your experience.  I suspected that a long length of any wire would have an effect.