The set was digitally remastered, but the results are wonderful to my ear. I also have the originals, and the box sounds noticeably clearer and cleaner than the originals, and, fortunately, not like the horribly remastered and also remixed CDs that came out some years back. Those remixes just sounded wrong to anyone who had grown up with the original mixes.
You can read details and some reviews here: http://www.elusivedisc.com/prodinfo.asp?number=WBLP74881C
The analog/digital restoration process is described here: http://www.elusivedisc.com/TheDoorsVinylRestoration.pdf
It looks like they still have a few copies left. Perhaps anyone else with the vinyl box can chime in with their impressions?