To answer the OP's last question, You can do both. But as said above by drewfx,  use the trim control and not the fader. If a recorded track is low you can tool copy it into a wave editor and normalize it. I do this for almost all my live recordings. Not for just the normalizing but general wave editing. Killing spikes, eq, remove boo boos. Sonar does not include a wave editor and Sonar's normalizing and gain function is terrible. 

Highlight the track and go to tools. Your wave editor should be on the list. If not there is a fix that has been documented here.