If you have more than one unit, can you use the same usb for both units?
If you are talking about the USB that flashes the box and puts BaseBuild on then yes you can as this USB stick is purely used to flash the box and import your line.
If you mean the box in the back of the box, not really. The second USB in the rear port is left in as it is where your recordings are kept along with other bits and pieces.