Do you mean that the D600 works the same as the D5100 in Live View mode? On the D5100, you must set your aperture before entering Live View, and you are then unable to set shutter speed manually. The way to work with this on the D5100 is to shoot in Aperture Priority mode, preset your shutter speed to 1/60 sec (or 1/50 in PAL regions), and use auto-ISO to set your exposure via the light meter. You can then make fine adjustments with the Exposure Compensation button. Once you get used to the semi-manual controls, it's actually quite convenient and compensates for the lack of a Live View histogram.
The d600 is better and worse than this. For one thing, I cannot get a light meter on the screen while recording. However, in manual mode everything is manual and adjustable EXCEPT aperture, unless you have a lens with manual aperture control.