Can anyone assist. Is this a case of waiting for a new Camera Raw update which includes the D750?
I can open in Nikon NiewNX2 but then can only export to TIFF.
There is no such update as of today. (Probably, there will be an update in the future).
What you did, convert to TIFF, is the only way to get the photos into Lightroom at this time.
Retrieving data ...