Not sure if I agree with this argument. Non-linearities in the analog
domain will not only produce higher (integer multiples of the base
frequency) harmonics, but also lower ones if the signal contains
multiple frequencies (this is called intermodulation distortion,
see http://en.wikipedia.org/wiki/Intermodulation ). So even in the
analog domain, a non-linearity may produce distortion components
that have lower frequencies than the original input content.
In practice, however, I these distortion components are often
masked by the audio signal itself, and hence you won't hear them.

Do you know guys if the Toneboosters Barricade employ oversampling under the hood? Would be cool to have a switch for multiple modes though like 2x, 4x, 8x.

Ask the man himself above Peter