I don't get how the circuit will function differently by shifting the ground reference. Let's just say that everything in the DAC ran on +15v. It would still run on +15v if I shifted the ground to -220v.LOTS of them. It is a trivial matter to throw together a circuit that is not going to like what you are doing. It requires much more care and effort to make one that doesn't care whether you do what you are trying to do or not. In order for what you are trying to do to work safely all-but-requires that the person that designed that DAC specifically set out as one of the primary design objectives to allow someone to do what you are trying to do. Did they do that? I have absolutely no idea whether they did or didn't. It all depends on what is inside that box! Our crystal balls simply are not good enough to allow us to guess what is in there.
You're being arrogant. I'm not convinced of anything, I'm trying to understand.He is going to anyway because he is convinced he is right.