Personaly, I would use a 3rd-party renderer like VRay, Mental Ray, Final Render, Brazil e.t.c But that's just me, I have more of an understaning of these and it is easier for me to get a result with these than it is with the default scanline renderer. With your renders the first thing I noted was the lack of focus, or the lack of bits that are drawn away from the focus to be a bit more accurate and also the ground is a bit offputting. What I would suggest with this piece, is have a fully white background, or fully black, with the ground to either reflect it the piece, or have just shadows, not a falloff of light or anything. The focus should be on the piece, not on the dark falloff of shadow on the ground. With the actual lighting and piece itself, I would reccomend deeper secondary shadows. For example, in your last render it is like everything is too well illuminated, It makes it look fake and plasticated and uncomfortable to the eye. The textures and modelling I think are great, it's just the rendering and lighting that is letting you down.