The only time I sanded a ball was when I put my EPX through the dishwasher..
The reason was that the lanes polished the surface to such an extent that I wasn't able to get all of the oil out of that ball. Once I removed the "shine" off that ball and then gave it the treatment, all of the oil finally came out..
So, my take is that IF you have a solid with a low grit OOB finish that you're doing an extraction on, I would first take in back down to the OOB surface..
JMHO that worked for me..
Yes. it's I, the Inverted One..