The D600 is not on the list of supported cameras for 4.3 and is apparently not listed for 4.4RC, either. Ugh. Maybe in the final version of 4.4. I seem to recall that 4.3RC and 4.3 final were not identical in some surprising ways. However the D600 does tether to Camera Control Pro which, by default, hands the file off to ViewNX. I imagine you could send the files to a folder watched by Lightroom and use LR as the viewer. You can try using Sofortbild if you're on Mac. On the PC side, at least ControlMyNikon does not yet list support for the D600. There may be others that do.