note THD is basically a meaningless spec for modern day amplifiers. nothing below 10% is audible to the human ear in car audio anyway. Also note that there are different types of distortion. solid state amps tend to produce odd ordered harmonics that are more easily heard and are thought to be harsh and unpleasant, whereas tube amps produce larger amounts of even ordered distortion, but this is interpreted as a warm sound that is desired by many people, such as in guitar amplifiers.