Years ago I bought a DJM-800 and contacted Pioneer several times about some bugs in the software and sound quality issues. FYI, I never got any reply back. I am going to address one here which I think is the most important one and has never been fixed to my knowledge, because even in the new 900nexus I still notice it.
This problem is distortion in the 3000Hz (maybe the crossover point) region when utilizing the EQ's on any given channel, when using any analog source. I haven't tested if it's also there when playing directly from digital input.
For example, when I play vinyl through the DJM-800 or DJM-900 (EQ-mode) and using the EQ's quickly or isolating a specific instrument in the high and mid frequencies in a rhythmic manner the distortion is added. The best way to hear it is to test with the high and mid pods, because it is more difficult to hear the distortion in the 3000Hz when using the low pod. Some would say that is normal because low doesn't reach to 3000Hz... but I am not sure it is band related. It is almost like the voltage going through the pods adds to that specific frequency when handled like mentioned above.
Any way I recorded it and send it to Pioneer. This time I got some response, but to my idea it wasn't really taken as a serious matter and even the add-on e-mail I send pointing out specific details was not replied back. This to me is very serious and that's why I am asking people here in this forum to test for themselves with their own DJM mixers to listen and see (graphical EQ) if they have the same issue, because I didn't test all of Pioneers products.
So with no more delay I will point out how to re-create the problems I experienced with the DJM-800' and DJM-900's.
I used all sorts of analog sources so any will work for others also (Line-in, Phone). Furthermore you could record the test for future investigation to see in a graphical EQ program whether you have the problem or not. (maybe it is firmware related) If you are ready to test just play any track, listen (preferably with headphones) and just randomly or rhythmically turn the knobs (all the way minus and plus, so watch your output in the headphones for example). Try different things like, killing the high's, leave low in the middle and then play with the snare in the mid frequencies... be creative and whilst doing this listen for any added noise that wasn't there in the first place.
When you recorded like I did, look for the peak in the 3000Hz. You will not hear of find anything unless you tweak the EQ's for example like Joe Claussell, Derrick May, or Theo Parrish :)
I've added a screenshot where it shows a little peak of the added noise in a part where I heavily tweaked the mid pod.
This screenshot shows that in the lead-in to when the track starts (vinyl) I already started to tweak and the peak is quite audible.
I am really curious if it is in all the DJM-mixers.