@Bradyhancock > I'm really confused here. Did NI tell you to connect a cable from your Master Out into another channel?
If so, it's not necessary to add any additional cables to the DJM-900 in order to record directly to your computer.
You will need to connect the DJM-900 to your computer via USB, and could you please follow these 2 videos below:
Please follow the information provided about the DJM-900 HERE
Please substitute the DJM-2000 in this video for the DJM-900 HERE
Please let me now if that helps you out.
I can't exactly go through everything at this moment, but hopefully those can explain it better.
In my personal opinion, I would use the DJM-900 connected via USB to record into Audacity (freeware) as I find it's a better application for recording and with more capabilities and exporting options.