@Tom > You need to configure the audio settings to be in EXTERNAL mixer mode, and have the Traktor decks output their signal on 0/1 and 2/3 (or 1/2, 3/4 depending on how it displays on your computer). If you haven't loaded the TSI file for the CDJ350, you'll need to do so. Don't forget to assign a different MIDI channel for each deck and you may need to customize the TSI to adjust for this.