Hi Scott,
The DxSA/B are not points being collected/added to a pointing model but is an on-the-fly adjustment to reconcile the point model against actual sky position. It is changes in DxSA/B which allows the mount to converge on the target during a “Centeri Now” operation in SGP. That’s my understanding of it at least.
Not sure about the Southern Hemisphere RA drift problem - don’t recall seeing anything on that before. But I am a “Northerner” :=)
There are others on the forum who can make better suggestions than me, but when I see drift like you describe, I usually put it down to either weight imbalance or polar alignment issues. There are some good tools out there for dialing in polar alignment, such as Polemaster/Sharpcap but those can still be fine tuned by using drift method (such as PHD2 Drift Align tool).
Perhaps also worth looking at your Dec backlash.
DaveNL