S4 Volume Problems - More quiet then CDJ on the same Level?

[Hardworx]

I do not encounter this Problem everytime, but often enough that its really bothering me. I connect S4 into Club Mixer on Line-In Channel, carefully adjust gain so im on the same level as Dj currently playing. Dj stops i press play and its more quiet then it was before from the CDJ (same musical style). I have to crank up the gain even more going badly into red to get the same amount of loudness, needless to say im hitting the limiter of the club making it sound pretty bad. I dont know what is causing that...

In Traktor the Master is not even in Yellow and im on -6.5db. I never could Replicate this Problem at Home, even if i play the same Track on CDJ and S4.

Anyone has an idea?

[Scalage]

Turn the master volume of the S4 higher. You're hitting the limiter on the mixer, but not on the S4. Therefore, the S4 is too quiet.