[gte460z]

Class AB amplifiers have a much lower THD (total harmonic distortion) than class D amplifiers but class D amplifiers are much more efficient (less power draw for the same output power). The higher THD of the class D amplifier is caused by the modulation used. This is usually only noticeable (to the ear) at higher frequencies which is why they are popular for powering subs. Most of the nicer class D amplifiers have feedforward feedback networks to reduce the THD to almost equivalent levels making them much more appealing.

In summary, a nice class D amplifier will be more efficient than a class AB and have similar audio characteristics. A crappy class D amplifier will have a high THD. The JL XD400 will be of the nice variety of class D amplifiers.