Is the sound quality from the integrated audio interfaces all the same in this 3 dj-contollers or are there differences?
there are no differences in sound quality, apart of that, S2 and S3 offer a sample rate of 44kHz/48kHz, while S4 also offers a higher sample rate of 96kHz.
Size and options is not my theme, i only want to know if there are (big) differences in the sound quality of the build in audio interfaces. I am speaking for use in clubs with capacity 300 - 800 people.
Size and options! ...for start :-)
Check by yourself:
S2: https://www.native-instruments.com/en/products/traktor/dj-controllers/traktor-kontrol-s2/specifications/
S3: https://www.native-instruments.com/en/products/traktor/dj-controllers/traktor-kontrol-s3/specifications/
S4: https://www.native-instruments.com/en/products/traktor/dj-controllers/traktor-kontrol-s4/specifications/