Can I use Pan Module (fka Pan PRO) underneath a SliderPLUS v5?

No, SliderPLUS cannot be attached on top of a Pan Module to rotate the whole setup. We recommend mounting the SliderPLUS directly on top of the tripod. You can see an example of what the setup may look like below:

Since SliderPLUS can slide twice its length while being used on the tripod, the slider's stability becomes more dependent on the support provided underneath. That's why we recommend SliderPLUS to be mounted directly on top of the tripod. Pan PRO is not designed to be a panner for SliderPLUS.