Traktor Output Volume

Hi,

i think i recognized when im using my sennheiser headphones to listen music in itunes it has a decent volume which i have set.
as soon as i start traktor and start playing tracks in there the sound in my headphones isnt that loud as with itunes.. why is it like that?
Its also the same if i connect my macbook directly to my djm 800.. i have almost to pull the gain for the channel to the max level..
In traktor i have set all values as default.. also the volume on the macbook is at 100%
and on my maya usb 55 soundcard i have set the sound output to 100%

Anyone knows why this happens?