According to this document:
http://akwww.digidesign.com/support/...48BitMixer.pdf
the Digidesign plug in bus is 24 bit, with each plug upsampling, doing calculations at 48 bit, and then truncate/dither back to 24-bit... Saying again; pro tools upsamples and truncates/dithers between each plug in at 24-bit. This is absolutely evil. See page 2, read end of 3rd paragraph of this docment.
If you want to approximate how bad this sounds, load three or four dither plug ins (set to 24-bit) onto the output of your 32-bit mixer. Listen to the shine in your cymbals roll off, listen to stereo imaging in the mid-range. It explains to me why the digi dithered mixer is not mandatory, when dither should normally be done as this dithered mixer does just before the hardware output (there is so much 24 bit dither noise in the signal already, it just isnt needed at the output)
And getting back to 32-bit, It is a huge deal. The 32-bit mixers maintain 32 bit instead of 24 bit as digi does for much of the process. Plug-ins all handle any dither or truncation at 32-bit.
Digidesign ticks me off because they wasted 3 years of my life and charged me quite bit for it. I have these useless, double priced TDM plug ins that sound horrible. It is a horribly designed mix engine. I can't believe that they released this white paper and proceeded to explain how bad there design is...
deep breath........................
As far as dither preference, I don't do any noise shaping. From what I understand, that is an option at mastering... I do not like UV-22 hr at 24 bit. My UV22 plug does not give me a 24 bit option. I am dying to hear POW-r dither at 24-bit, but I don't think they are going to release any plug ins....It sounds like they are going to be OEM only...My only option is Nuendo's built in dither. It is better than nothing.