Hey Mathieu,
I guess it would help to know what the intention is for using the MIDI keyboard with the software ... are you trying to use it to control rekordbox? Or does that keyboard have an audio output that you're looking to add to the mix? If it's only audio, you would just route that to one of the inputs on the DDJ-1000 (eg. CH3) and you could do the same for your drums (CH4) so you can control them independently and EQ / effect them as well.