The alleged advantage (I'm not entirely convinced of this, but I haven't done a definitive test) of the general stain with PMK is grain masking, since pyro is by nature a grainy developer. Read Gordon Hutchings' _The Book of Pyro_ for all the details.

If you want to decrease the effect, don't do the pyro or sodium metaborate afterbath following the fixer and reduce your wash time to 10 minutes instead of 20-30 minutes recommended to increase the stain.