Q:
Why does a signal at 0dB on my console not show up as 0dB in my DAW?

A:
Different types of dB are used in the analogue (dBU) and digital domain (dBFS) and therefore you will see what appears to be a 'lower' signal in the digital domain.
Usually you will see that a signal at around 0dB on the mixer will show in your DAW at around -18dBFS. 

The signal is not actually 'lower', it is instead being expressed in a different unit., 
so the signal should not be boosted to try to achieve 0dB in your DAW as you could incur distortion in the digital and/or analogue domain.

(see Wikipedia article for more information)