convert 16 bit tiff?

I am trying to recover disk space and have been using the DNG Converter to save 10-20 percent on my Canon cr2 files

I also have over 256 Gigs of 16 bit tiff files that I have outputted over the years from the HDR program Photomatix Pro,

When I originally saved them I saved them at a bit depth of 16 so I would have more to work with for the final editing.

So, on average the tiff  files are each about 100 megs, I am guessing that as a DNG , it would shrink that by about 75%

DNG converter doesnt like the 16 bit tiffs and skips them.

Is there another piece of software that can convert 16 bit tiffs to DNG

OR

Is there another piece of software that can batch convert 16 bit tiffs to 8 bit so I can dump  then them into the DNG converter without having to do each file one by one.

Thanks

Todd McIntosh