it looks like hues on your specular map are the same as hues on diffuse map. this can work well for certain materials however stuff like varnished wood or rubber cable should have more or less white highlights. to achieve that their hues on specular map should be the opposite of original hues.
The alpha is in the diffuse and doesn't look like that at all. I mean, it's basically all white except the little black rectangle surrounding the needle, because that's basically the only thing that is on a plane. Anyway, sent an email to Marmoset about that. In the meantime, I finally got around making something somewhat…