Thanks. That is helpful. The internet is full of discussions on this such as:
http://recforums.prosoundweb.com/ind.../t/15038/6263/
and the protools mix bus is nicely explained by digidesign here:
http://akmedia.digidesign.com/suppor...ixer_26688.pdf
And it seems the consensus is to keep levels low because there is room to spare.
And it seems that while the mixer has 12 db headroom (due to 48bit internal precision), the bottlenecks would occur when a) bouncing to disc, b) outputting to a DAC, or c) feeding the signal into a plug-in. These are all instances where the 12db headroom is removed, if my understanding is correct. I guess I was just surprised that I can not hear the problems with a hot mix, even peaking at +3 on the master fader - perhaps my ears are what's lacking.
Thanks!