Class AA is Technics version of "non-switching" amplification. In a proper Class AB amplifier, at some signal level, the amp operates in Class B with only one output leg active. In Class AA, the inactive leg never completely shuts off, but stays in Class A, but with a significantly lower idling current.
Very similar technology is used in JVC's "Super-class A" amplifiers. The result is usually an amplifier with reduced high volume distortion than Class AB when a class AB is in B mode, but more distortion at low volume levels compared to a Class AB.