The RAW is 14 bit so any display is an 8 bit interpretation of it. I assume the tiff is an 8 bit version ? As long as the RAW is read in a fashion that operates on 16 bits per channel, nothing should be lost (Sagelight does this, GIMP doesn't do it fully yet).
The first article in this blog discusses RAW processing: http://sagelighteditor.wordpress.com/
"Before I researched it, I didn’t realize the extent to which many RAW conversion programs will damage your image before you even see it."
Perhaps the next step for your package is to read RAW's and process in 16 bit per channel ?