Then I added eyebrows (hmif018), lips (hmif021) from miscellaneous facial human maps from the and a scratch to give him personality :P(V4).
Afterwards I added some other human maps to simulate wrinkles in the forehead, around the eyes and next to the lips. I also added a beard with a grey hue area and some transparent dots made with the brush tool using a multiple dot brush type.
Next two steps should be better done when high poly model is created so you can skip then and come back after.
For the outlines of the face I first added a layer with hard mix as blending mode over the hsky015 layer containing the baked light of the model with a three light illumination set up.
Then the last step was creating another hsky015 layer forehead with luminosity as blending mode and 65 % of opacity and use the burn and dodge tools to simulate the light and dark areas of the face. This process should be done while looking at some reference photos in order to know where those light and dark areas are. If you don't need them, then you're a master :)
For the neck I used the same skin base then and put the hole wounds and a tattoo (multiply, 65% and dark green color).
Creating the head pieces
All head pieces are a mixture of several textures within total textures sci-fi V7. All texture layers are used playing with layer blending modes and opacity.
For example, for the brain area, where it has a grey metal texture I created three layers and added a border lighten part.
You can see here the final color texture.
For finishing the overall texture I added some image adjustments such as Hue/saturation, it's always a good advice to play with them after the texture is finished which can lead to nicer results
High Resolution Model Creation
Exporting and importing process:
Select the mesh and export with max OBJ exporter with these settings:
You can export only the original (not mirrored) parts of the mesh or mirror them and export the whole mesh. I recommend the second one, and then play as much as you can with the symmetry options within zbrush. That way, you won't have seams when creating the normal and bake textures from the high resolution model. If you don't do it, then you'll have to touch up much more the seams during the texture creation process.
It is important to use several digits, if not texture coordinates won't export properly.
Inside Zbrush, import the mesh (Tool->Import) and apply the texture already created (Texture->Import), the same texture you used for Max model.
If the texture is not well applied to the model, flip it vertically (Texture->Flip).
Now you're ready to work with the model in Zbrush seeing the texture applied in order to see where you wrinkles, for example, should be.