Official comment
@Potofx > The SP1 is pre-mapped for certain functions; the CFX are not one of those pre-maps as that function would be controlled by your mixer or controller instead of the SP1 as it doesn't have those extra knobs.
If you wanted to do it, you could configure the sampler volume (for example), simply open the Sampler section of the MIDI panel, then remove the B603 assignment (sampler volume), then go to the FX page and add a CFX Parameter option (any channel or the master), then use the LEARN button to assign it.
