Francisco,
I have a few suggestions:
If you are running the latest version of Final Cut Studio, in Soundtrack Pro - change the Normalize function to RMS. As a starting point set the slider to about -16 dB and process. Keep in mind RMS Normalization will affect the average volume. Very different compared to Peak Normalization.
Also, check out the Levelator. It's a stand alone tool designed to process spoken word segments.
http://www.conversationsnetwork.org/levelator/
-paul.