The inputs of the NI-4472 are pseudo differential. The User Manual contains a schematic of the analog input for the 4472 (
link to 4472 User Manual) on page 3-3. Because the inputs are pseudo differential, we don't recommend using a ground which may vary by more than +/- 2.5V from the ground of the 4472. This would cause a ground loop to occur which could impair measurement quality or even damage the device.
What is the output of your amplifier? Is it differential? Could you use a single ended amplifier?
-Jack