It is configuration A. Balanced signals have 4 incoming signals, related to ground. Single ended (RCA) has 2 incoming signals, related to ground. RCA has no negative signal, only ground. In the balanced 4-gang pot, when you make one click, it reduces the incoming signal on + and - for left and right channels the same amount. You could replicate that by using 2 stereo volume controls. One for left, and one for right channel. For the left channel, as an example, you would use each gang in the pot for the + and the - signal, with the wiper being a voltage divider to ground for each gang. That is configuration A.
The amp you have is not differential, so wiring in an XLR is somewhat pointless. The input transformer converts the signal to single ended for the amp topology. The gungnir does the same in it's output stage. DACs are differential in nature.
If you put the pot after the input transformer, then you would have familiar wirings, dealing only with 2 signal channels, Left and Right (again there is no negative only "positive" signals which is the combined signal).
Configuration B (or the schematics I posted from the Monolith amp) controls balanced signals with a stereo pot. It alters the impedance seen by the source, however. It is no longer a static 10K, but will vary by wiper position. The inline resistors limit it to something manageable. This is, in effect, what is known as the shunt mod (if you didn't have a negative signal).
I hope this helps. It's a bit confusing.
Morgan Jones has this in his books too. I can see if I can dig out the text and photocopy it, but it might be a few days or weeks before I get to it.