Waw28SVX v2.0.1 released, new code is roughly 37% faster than 2.0.0. Links are the same as in the opening post
I tried it, the sound is less muffled with this way.
However with this method the conversion was 1.7 times slower than the former sox converting method, 7.5 times slower than wav28svx 2.0.0 and 10 times slower than wav28svx 2.0.1.
Dithering no, resampling yes, but only if you specify the destination frequency, else it will only mix the channels (if there are more than one channels).