Recordings are not loud enough

Hi there,
We have been using WaveLab 8 for over a year now, and are really happy with it. Except that our recordings are too quite compared to other recordings. So if we listen to a Cd for example with mixed recordings from different sources, every time a song from us is played we would have to turn the volume up. We have maximized the input loudness we get from our mixer. The quality of our recordings is great. When we do a recroding we keep the moving input bars L+R in the middle zone, which is set from -2 dB. The top zone is set to +4 dB. Any suggestions what we could try to bring the loudness of our recrodings up? Thanks in advance.