OK, had a crack at removing the blender node and simplifying the other nodes and got this;

which is a huge improvement, if somewhat transparent. This still has the transmaps at a gamma of 2.2. If I change them to 1 it gets a little better, but you can still see his skull through the hair. After that I tried ajdusting the transparency setting in the various material zones and with a trans setting of 0.2 got this;

so as you can see the hair is much less transparent but all the marks are back. I should also mention that the hair has 2 overlapping material zones, a scalp mat and a hair mat, both with trans maps.

My uneducated guess (question) is... could the light be bouncing between the transmaps and showing up like this? I think I can get a generally acceptable result now, but lacking density. I'd like to improve it further if I can, though. Besides, more knowledge!