The ONLY place I know of cathode bias being used in a Class AB amp is in a very few certain guitar amps, and only then to net a certain, unique sound when the amp is cranked. But then again, I don't know everything........But, even in that "special situation," the power tubes' operating point is still set pretty close to Class A to prevent it from completely "throwing water on the fire" when the amp is cranked.
Thermionic