Only works with internal amp.
Not to say an enterprising person couldn't do exactly this with a DSP engine and any other amplifier, but we might argue if it is even ever needed elsewhere, especially if your other amps are analog.
As I understand it, this is a way of using feed-forward techniques to compensate for the inherent non-linearities in the Technique's output filter, and perhaps other issues as well. It's kind of an EQ for the amplifier under load.