I should probably quote message from Kingwa "The Master 6 if high current output stage, its configuration made it without switch distortion so it should be a class A amp."
So as far as switching distortion definition of class A is concerned it is fully class A. This is the present definition of class A.
As far as the older definition of class A (this older definition refers to the amount of current available at the ouput stage), [the Master 6 is] class A output is 400MW at 100 ohm and Class AB is 3500MW at 100 ohm. For any sensible listening level, even with the HE-6, the Master 6 will still be class A even by the old definition.
AFAK class- A aspects have not changed between Master 6 and Master 8.
EDIT: I have hopefully clarified this post.
It would have been nice to know what the output level is in the old definition in 50 Ohms. It should theoretically be double as much (800mW), but usually it's not. The Master-6 is in fact spec'ed to double the output from 100 to 50 Ohms: 3,5W to 7W (in class AB).
The Master-5 is spec'ed at 2400mW class A in 100 Ohms, so things are looking a little odd here ... The Master-6 ought to have more power than the 5 - even in class A - or what?
(scroll down to the bottom of the page to see spec's.)
Anyway - if it sounds wonderful - who cares? Hmmm ... the fools like me do.