Confusion with grounding floating sources to be used with a differential ended data acquisition board
You have to ask yourself what common mode voltage might appear between "earth" and AIGND: -



Then you have to check whether your DAQ differential inputs can handle this voltage both safely (without destruction) and without unacceptable performance degredation.


  I wired the DC- to earth ground, but is this correct? I'm not sure
  whether DC- or SGND must be wired to earth ground.


If both are internally connected inside the transducer (as per the dotted red line above) then it won't matter.