1 Ground the rig . Create a wired connection to a diy plug. Plug it to a grounded socked on your wall. Make sure your electrical socket on the Wall is actually grounded properly. do that check with a voltmeter (sometimes that s not the case if done by a lousy jobber)
2 Ground the DD wheel , especially the motor with a wire to the rig or to a wall socket
3 ground each device , to avoid flickering etc
that should be enough.
PS the Dennis Reimer usb mod is ok as long as your rig is also properly grounded . what it does is make a connection between the shield and GND of the device to the GND of the rig that is also grounded. in a nutshell everything should be connected to the electrical wall socket GND one way or another...