CDJs different output volumes

Hello,

i’ve got a few technical question considering the audio sound card in the pioneer CDJs. As a DJ, I always used to play with the Traktor software from Native Instruments together with their audio interface 'Traktor Audio 8‘. If you compare the sound quality and especially the output volume of any of the Pioneer CDJs to the traktor sound card, the CDJs are a lot better than the traktor sound card. Since most of the clubs configured their limiters with the audio signal of a Pioneer CDJ, I’ve always encountered the problem, that my output volume is beyond the volume of the DJ, that played before me with Pioneer CDJs. And it’s not only the volume, the bass seems to be a lot more 'fat‘ and rich. This brings me to my first question: Is it just the good quality of your audio interface that leads to such a good sound or do the CDJs add some kind of compression to the track? Since it really bothered me loosing the people on the dance floor because the volume was not loud enough, I tried to connect my traktor software with two CDJs 2000 as sound card. Everything worked out fine, the track is played in the Traktor software and send via USB to the CDJs. The audio sound card converts the digital signal into an audio signal and sends it via chinch to the mixer. But the desired volume boost came to nothing, the track had exactly the same output like my traktor sound card. Then I plugged a usb stick in the CDJ with exactly the same track i played from the traktor software. And behold, the volume was much higher and the bass much fatter than when I played the track directly from the CDJ. I switched back to play it from the traktor software with the CDJ as audio interface, and the sound quality was weak again. The mixer had on both channels exactly the same settings, i even switched channels to see if the mixer causes the volume loss. But it seems that tracks played from an USB stick are a lot louder than track played from the external input. How can this happen? I thought both signal go the same way through the sound card? Is there a way to boost up the sound when i use the external input? I would have already switched completely to CDJs2000 nexus if it was possible to change the tone (key) of a track without changing the tempo. Well i know there is the master tempo which freezes the key of a track at it original value but there is no way to change this parameter to a desired value. That’s why i’ll stick with traktor and try to use the CDJs as sound card.
I hope I can find help with this issue, thank you in advance for reading this long text and i’m looking forward to get your answer.

EDIT: I've just installed recordbox dj and and tried the same scenario with this software instead of traktor. And there is a big volume difference as well. So i guess the volume of the ext input is internal somehow limited?