My final gather settings was disabled, I even didn't know they existed. But now I will turn this section on and test the values to see what happens. Altough this, I think the render is clean, except by the skin. But by my fairly poor knowledge of SSS, I think this is related to my lighmap settings, that I forgot to update before do the render. It seems I have to adjust the values of File Size Width and Height, depending of my camera resolution.
What I'm calling Epidermal map, for the lack of a more apropriate term, is the one I'm using on the "Subdermal Scatter Color" channel. I believe it's not the responsible for the dryness. I guess I reduced specular values too much, and this is the problem. I'll do more tests with this today. About negatives lights, Legolas_hv are sugesting I make use of them. But I think I wouldn't, time for testing things is very little now. Maybe for the next challenge.
Thanks for your offer about doing light tests with my model. But this is the kind of thing you have to discover by yourself. Your help is being extremely useful, and by now is enough to me. Many thanks, man!