Mark Levinson 436 Monoblock Amplifiers- How much Class A?

Don't know for sure but, in general, a class A/B amp will operate in class A up to where the output current is about twice the bias current. The ML 436 idles at half the rated power output at 8 ohms so I am guessing that means it's biased close to 1 amp. Therefore the class A operation is twice that squared times 8 ohms or 32 watts.

That's a guesstimate.

@OP
HERE IS THE STEREOPHILE REVIEW :

http://www.stereophile.com/solidpoweramps/905/index.html#vCsVLcdO83yIrFHM.97

Excellent points,
gs5556 and lucidear. This is a very powerful amp.

I apreciate the information. Thanks gs5556!  No luck in the stereophile review. 
Agreed, they are powerful amps and I have been very happy with them for a couple years.  Great low end, mids, imaging and dynamics.