Adjust your final output level with the master fader.
For more info read this;
http://www.digidesign.com/digizine/a...il03/techtalk/
(excerpt)
".....there is no data, or information, lost while mixing completely in Pro Tools, that no signal is lost when you pull a channel fader down below unity, and that there is no difference between setting all of the channel faders to -30 with the master at unity and setting the master to -30 with the channel faders at unity. As long as you're not clipping the output and are sending the highest possible output signal before clipping, then all is well."