Pass A vs. AB amps

Could it be that the only difference between the Pass Labs class A amps and the AB models is simply how much they are biased into A? I'm not an engineer or a technical person but I know that the AB models (e.g., the X.5 series) are heavily biased into class A. They run quite warm, almost as warm as the XA.5 series.

Can you simply adjust the bias of a X.5 and effectively convert it to a XA.5? I once owned a Forte class A amplifier that I could adjust the bias, with successful results.