Using the distance filter is a good example to start from. The function FMOD_DistanceFilter_dspsetparamdata is part of the FMOD_DSP_DESCRIPTION, so it is called by FMOD when a data parameter is set into the DSP.
If you place the plugin on the master track of an event, and if the DSP has declared a FMOD_DSP_PARAMETER_DATA_TYPE_3DATTRIBUTES parameter, then FMOD Studio will update the 3d position into the DSP when the emitter or listener moves.
The data type that is passed in is documented here:
http://www.fmod.org/documentation/#content/generated/FMOD_DSP_PARAMETER_3DATTRIBUTES.html
It doesn’t provide the listener orientation, but it does have both the absolute and relative position of the emitter (compared to the listener).
If you want to support multiple listeners, you can declare the type FMOD_DSP_PARAMETER_DATA_TYPE_3DATTRIBUTES_MULTI instead. Then you will receive this structure passed to the callback:
http://www.fmod.org/documentation/#content/generated/FMOD_DSP_PARAMETER_3DATTRIBUTES_MULTI.html
That structure contains all relative orientation for all listeners.