IDR and dithering?

Hi
I've been using the waves gold bundle with the L1 Ultramaximizer and the C4 in Sonar.
Now, I'm really happy with what especially the L1 can do my mixes in terms of dynamics and limiting, the same goes for c4.
But my question is about IDR and noise shaping.

The way I've understood it is that the plugins operate on i.e 64 bits, and then we dither it down to 16, leaving some noise on higher frequencies by taking the extra bits and in some way crunch it down into the 16 bits(how is this possible anyway)?
When in the process does this happen? The signal coming through my master in Sonar isnt 64 bits? Or?
Also, I hear a difference in sound when playing projects in Sonar and when playing the mixdown in a media player.

Also, I'd really like some extensive information about IDR and noise shaping as I dont fully understand these functions practically.

A lot of questions, and any help would be very much appreciated.