Pass Labs Xa60.8 Class A or should it be called class A/B?

All ‘class A’ power amps transition to A/B at high levels!

Sorry not true.  The distinguishing characteristic of a true class A amplifier is the quiescent current is at maximum with 0V output and to produce output away from zero the opposite leg's current is reduced.

An amp that transitions has some quiescent current far below maximum which then is INCREASED above a certain threshold during which the opposite leg eventually shuts off.

These are the two required characteristics for a true class A:

• Maximum current and power goes through the transistors at 0V
• Neither transistor side ever fully shuts off.
  

There are a number of Class A amps which fulfill this requirement.

Of course this makes true class A amps monsters in terms of electricity consumed and heat output.

I also want to point out that it seems Luxman also does a similar thing with the L 590, but I'm not entirely sure.  They sell it as a 30WPC integrated but measurements indicate it can do much more around 100WPC.  Perhaps it is also a "high bias" class A/B?  It is also possible it is a true class A amp but can't handle the required preconditioning load so they instead underrate it.

Let's think about it the other way round.

How many amps described as class A/B offer 122w of class A power?

I'm puzzled as well, since peak power of 60W sinewave is 120W.  Most of power comes from low frequencies and it is likely to be close to sinewave.  Does it mean that headroom of this amp is only 2W?

Could possibly/ likely be 60 watts of class A into 8 ohms and 120 watts class A into a 4 ohm load.
Charles 

From JA/Stereophile, 
"Specified as putting out 60W into 8 ohms and 120W into 4 ohms (both 17.8dBW), the XA60.8 considerably exceeded that power, delivering, at 1% total harmonic distortion (THD), 150W into 8 ohms (21.8dBW, fig.4), 240W into 4 ohms (20.8dBW, fig.5), and 380W into 2 ohms (19.8dBW, fig.6). The THD begins to rise above the noise floor at high powers, but remains at or below 0.1% below the specified output power. The percentage of THD then slowly rises with increasing power, suggesting that the XA60.8 has only a small amount of corrective feedback."
Charles