Tuyen, yes I think the differences were quite obvious, even through youtube/headphones hence I found it interesting enough to post.
I preferred C, seemed more natural if not a touch attenuated compared to B, perhaps the inductance of the autoformer. Pity not much detail was given how the resistors were used, assuming as a divider or part of, nor if any compensation was added for the autoformer.
According to their blog they will be posting another video showing the differences between core types in the autoformer (orient hi-b, finemet, amorphous), that should be quite interesting...