Maybe you need 'replay gain' instead of 'volume normalization':
replaygain <off or album or track or auto>
If specified, mpd will adjust the volume of songs played using ReplayGain tags (see <
http://www.replaygain.org/>). Setting this to "album" will adjust volume using the album's ReplayGain tags, while setting it to "track" will adjust it using the track ReplayGain tags. "auto" uses the track ReplayGain tags if random play is activated otherwise the album ReplayGain tags. Currently only FLAC, Ogg Vorbis, Musepack, and MP3 (through ID3v2 ReplayGain tags, not APEv2) are supported.
replaygain_preamp <-15 to 15>
This is the gain (in dB) applied to songs with ReplayGain tags.
volume_normalization <yes or no>
If yes, mpd will normalize the volume of songs as they play. The default is no.
http://linux.die.net/man/5/mpd.conf