These two spectral processors can be considered as being equalisers that have been especially designed for virtual sound emitters simulated in virtual spaces.
This filter section is for equalising the omni-directional part of the sound radiated by the virtual source. This equalizer mimics the global frequency response of the source, similar to how a loudspeaker colours the sound.
This filter section is for equalising the on-axis part of the sound radiated by the virtual source. Most, if not all commercially available loudspeakers do exhibit a radically different frequency response whether a listener or microphone is right in front of it or to the side.
Setting a rather flat on-axis equalizer curve, and maybe cutting the treble and mids for the omni response would be a good starting point to emulate a real-world speaker, so this is the default setting for these filters.
★ Spectral Axis performs more like conventional mixer EQ