Topic: Poor sound quality when connecting RPM to Pionneer DJM 800 dj mixer

Hi
I use my RPM interface to play with my dj software (Traktor PRO).
Whenever I connect my interface to a Pionneer DJM 800 mixer the sound quality is very poor : Very low dynamic range and random fluctuations in sound level (almost like a limiter compressor effect)
I do not have this problem when I connect to other mixers such as the Pionneer DJM600 for example.
Whenever another dj plays after me (even with soundcards that are not as upmarket such as the serato box by rane or the audio 4 by native instruments) I can really feel the difference, sound is much louder and dynamic range improves.
I have noticed this only when connecting to the Pionneer DJM 800 mixer. It is very very strange and I am unable to fathom any explanation whatsoever.
Can anyone help ?
All the best
Nick