Ok, multiplication by the scaling factor doesn't work. Whatever the conversion method is, it's not this simple. I've noticed the deltas for animated joint centers are not in the same scale, so the problem is not just with the joint center positions. For example, if I translate a joint center by "1.0" in the X axis in Poser, it only moves a tiny bit. In DS, on the other hand, it jumps off the screen. In addition, the NS morph also changes the bones length, so I would have to recalculate the end points for over 50 joints all the way to the fingers. So maybe the approximation I've got is the best I can get.
There is one last thing I want to try. Maybe if I use "Adjust rigging to shape" to fix the joints below the elbow, and then manually adjust the shoulder joint, this could fix the pose preset differences that happen due to the bone lengths being different.