Hmm, on the first one, the background doesn't work too well with the render IMO. On the second, well, I kind of have to see the stock. It doesn't look like you did much besides add the black rectangles and maybe a 100 px soft white brush in the middle.
I believe that with the first one, you should try a gradient map to blend the render in. I don't have much to say about the second one seeing how I've never really... seen something like that before.
Crop the empty space on the second one. The first one i'm not fond of, but theres really nothing wrong with it. Just not a good render.
Isn't the background in the second one from a sig? I think I've seen it, but I don't know where... and add some Adjustment Layers to the first one, looks a bit plain. Jazz it up.