I don't know if you noticed, but mine is also a 12 poly (not 8 ), 6 sided cube.
The normal maps are usually created based on a hi-poly sculpt or model and baked out via some tool. That is why I used xNormal and the hi-poly mesh from the download to generate it. I also baked out several other textures such as bend normal, cavity map, ambient occlusion map, height map and join them together to get a nice diffuse map.
Here is a great tutorial on how that works.
In the DOTA2 Texture tutorial (link above) it explains ( a possible way ) to match these models together
For the color I got a ref picture from the borg, took the lightest color and the darkest color ( just not black) and rendered out some clouds in photoshop as a base of the texture.
Generating a normal map from a picture works too but it is just not the same, there is a plugin from nVidia in photoshop that does that.