Hi Kieran,
You can't split the mic from the recout output, but you can send 3 channels and the mic back to the computer via the onboard soundcard. (the sound card is 4 channels stereo out / 4 channels stereo in)
go to the DJM Control panel, and on the output section select:
USB 1/2 - post channel 1 fader
USB 3/4 - post channel 2 fader
USB 5/6 - post channel 3 fader
USB 7/8 - MIC
Then go to your recording software and select the corresponding channels.
With this setting you'll be sending the 3 first channels and the mic back to the computer.