Before you add your curves layer, try and select the entire background with a selection tool. If you add an adjustment layer with a selection active, the layer will use your selection as its layer mask, and thus apply only to the pixels in the selection. This will also leave the colours in the actual screens untouched.
It looks like the Magnetic Lasso (L, press Shift+L to cycle through the different lasso tools or the Quick Selection (W, Shift+W) tools will make quick work of selecting just your background.
Things might get a bit shifty in the shadows: try including them in the selection first, but if that doens't work out to your liking, try excluding them or giving them an adjustment layer of themselves altogether.