HD Geo color info should be included as part of the normal color texture generation process when generating a map from polypaint. The texture must have sufficient resolution to hold the detail.
A Matcap is a surface shader, not polypaint info, however. Most of the look of the matcap comes from from the lighting information which is baked into the matcap (which is not what you want if you want to light your own scene). I know there are methods to approximate the look of a matcap in a texture (keyshot does this with the keyshot bridge, and converts the matcap into a color approximation in the program.) However this is not my area of expertise, and I can’t advise you on it.
My advice would be to forget the matcap altogether, and fully paint the model, rather than relying on the matcap to supply the color. Use a white matcap, or one of the non matcap materials for color painting. It will just simplify the process, and probably provide better results in the long run, as matcap colors are very simple without the lighting information, whereas skin textures have complex color schemes.