Enhancers use any combination of:What, exactly is it doing?
multiband/single band compression
harmonic addition
Band delays
Eq
Phase correction
distortion
stereo widening
You'll find it difficult to learn which enhancers do which (or which combination of several of them) as it's traditionally been one of those things that manufacturers and coders try to keep secret (traditionally because of patent issues). But some enhancers will use all of those methods, some only only a few - it's rarely only one process.
Alot of it is psychoaccoustics - affecting how you perceive music. To be honest, I never was that bothered about how each processor did it - you simply put your mix through a black box, magic happens and better music comes out the other end. You either like a particular flavour of enhancer or you don't. Witchcraft is witchcraft and best just left alone
