DUT-to-Scope wiring (i.e XLR balanced-to-BNC) might be more complicated though
Indeed, there really is no way around needing to know what kind of output you have.
There are four types to consider:
1. Transformer
2. asymmetric, balanced impedance
3. symmetric, independent output drive
4. symmetric, but cross-coupled output drive
Most of my gear is either transformer balanced of IC balanced (that12xx) so I believe that fig.6 would be the right solution.
Yes, and take note of the footnote that indicates pin 3 connects to pin 1 only for cross-coupled output stages. Transformers are fully floating, so it should just be pin 2 to center conductor, pin 3 to shell of BNC.
You can also do that for asymmetric, balanced impedance outputs. That type has pin 2 driven, and pin 3 connected to the output circuit local reference ground through components to match the impedance as closely as practical (so usually a resistor and capacitor to match the components on the output of the op-amp driving pin 2, and possibly EMI filtering components).
What I called type 3, symmetric independent drive is just two op-amps, one driving pin 2 and an inverted copy driving pin 3. In that case you don't want to ground pin 3, because it would just result in one of the op-amps driving into a short circuit. Excessive power supply draw in the best case, device overheating and distortion injected into the other side in some cases.
You wrote ThatCorp 12xx above; were you talking about inputs, or did you mean That 16xx output drivers?
The 16xx drivers are a special case of cross-coupled outputs. The original simpler design is much easier to see. I believe the origin of the design was from an HP paper back in the 70's, but it became popularized with the integrated implementation from SSM/Analog Devices, and now the TI copy:
TI DRV134 product page
Note in the diagram the feedback connection from +Out back to the amp driving the -Out pin, and the feedback connection from the -Out pin back to the amp driving the +Out. The feedback connections "cross" (and of course there is the usual negative feedback as well).
That was an attempt to mimic the behavior of a transformer, where if you grounded pin 3, the signal at pin 2 increased in amplitude, so that the output amplitude was the same whether you were driving into a balanced or unbalanced input. It worked in that regard, but because of the feedback path back to the input of the driving op-amp, grounding at the far end of a long cable, which would add some delay and a lot of capacitance, could make the output go unstable, so it still wasn't a perfect substitute for a transformer.
API came up with a design that improved on that behavior, and That Corp licensed it for integrated device use. The head technical guy at That Corp presented an AES paper on it back in the day describing the problems with the original, and how the new circuit improved on that:
That 16xx AES paper
One option not discussed in the Rane paper because it isn't really relevant for sound systems, is using two inputs on your scope and using the math functions to create a balanced input. In that case you need two coax cables thin enough to fit into your XLR housing, and the center conductor of one goes to pin 2, the center conductor of the second goes to pin 3, and the shields of both connect to pin 1.
At the scope you then create an internal signal which is first input - second input, and use that synthetic signal instead of the direct signal for the rest of the measurements. If you are using some kind of automated Bode plot software package on the scope you have to make sure it lets you use the synthetic signal rather than direct input. If you are calculating by hand then it is just a couple of extra setup steps. Of course you need an extra 'scope channel to do that, so won't work with a two channel 'scope.