You should try using a gloss map although, since it's marmoset, it's not so good at supporting those.
Sounds like marmoset isn't worth using then. Gloss is a pretty basic requirement.
or you could screengrab it in maya or 3dsmax, using a directx shader.
Or if you must, render it properly with scanline/mental ray.
Chicky Dip, paint your scratches, (or blend photos) to a seperate layer.
Once they look good, dull the scratches in the diffuse, ie turn down opacity level.
The Specular is usually a duplicate of the diffuse, but with emphasis on materials. Here the scratches would be at their brightest. Even with a bit of colour noise.
The gloss level of metal is generally low, maybe 15-25%.
Painted metal would have slightly more gloss.
The model seems fine, just jazz up the realism of the texture.
In POV view, its clear u need to sharpen up the wood.
Its tricky to get a balance of all-round equal UV space whilst making sure it looks best in POV mode.