Update: The grounding cable arrived today but does not fix the hum. On top of that I can't reproduce my temp fix using an RCA lead as a grounding cable anymore. Something is amiss. Back to square one.
@damien It's clear that the 96 is too much of a mixer for you. Perhaps you'd be safer with the training wheels of the Pioneer DJ range, and leave the 96 to the big boys like @astromech and myself.
Hercules DJStarter Kit is an easy-to-carry and easy-to-install solution includes the Hercules DJControl Starlight controller, Hercules DJMonitor 32 speakers, HDP DJ M40.2 headphones and Serato DJ Lite.