Since we use Loudness R128 to set the levels, "old-skool" audio tech like CD's will sound low since the volume settings on players usually compensate for over-compressed and normlized audio sources.
Our suggestion to fix this is:
1. Add a Master track
2. Activate the built-in compressor and set to level "1"
3. Turn up the Master Track gain to max (6 dB)
If you still find this too low, you can also increase the gain on the individual tracks.