It sounds like there is a compressor/limiter inserted on the DJ inputs, which is quite common, especially if the club has DJs who are not supervised by sound technicians, and who might otherwise blow up the PA system.
Talk to the person who is responsible for the sound system about patching in to different channels. They are unlikely to adjust or remove the compressors on the cables they have run to the booth area, because the abusive DJ will be back the next night blowing up the PA.