Filipe,
I don't agree with you. In all case (external or internal reference voltage), the reference is the AOGND signal (see figure 4-3 in the 6713 manual).
And it seems that the AOGND is linked to the DGND and to the ground chassis.
In fact I have seen this problem because I am using a floating source as external reference and when I connect this source to the 6713, the signal falls because we connect the ground chassis to the source.
I need that the AOGND will not be connected to the other ground reference. In this case I could supply my own "ground" reference.
Regards
Hubert Robitaille