For all of you Pro Tools users out there with 16 bit systems, here is a great tip from one of the Sweetwater Sales Engineers:

Recording directly to disk (ie creating an audio track and getting it's input from one of the analog ins of your I/O interface) with any of the 18 bit or higher converters on the market will cause a 16 bit Pro Tools system to simply truncate any LSB (Least Significant Bits) beyond the 16 bit word that Pro Tools can record.

If you bring the audio data into an aux input, insert your favorite dither plug-in across the aux input, send the output of that aux to a bus, and then create your audio track and get it's input from the bus you sent the aux to, you will be recording a dithered, rather than truncated 16 bit word.