I'm playing this "anti-English" right now in a Najdorf thematics tournament here.

a6 prepares also b7->b5->b4 counter-attack in the case of Keres attack g4, for instance.

a6 is made to enhance domination by black in its queen half....notice the control over b5 before a6 is moved(considering white bishop in diag f1 a6), u will see the significance of move...

The move a6 is the hallmark of the najdorf, i am not quite sure if this is a joke.

I don't follow the a6 move. Seems useless, unless you're just trying to pull out the bishop for an attack by the black knight.