I doubt the volume control will work, because the main volume control is probably not midi related. No midi message is being sent is my guess. I don't have an xp10, but I wonder if you can hook of a control pedal either to it or to the QSR, and set it up for volume. This way, midi volume messages are being sent. I don't know about the other sliders. Maybe the QSR isn't set up to recognize decay signals and the like.

By the way, how many threads are you going to start aboutt this anyway?