The purpose of this module is to forward calls made to HIDL API or AudioFlinger service to active hw module. This means that the module cannot be loaded independently, it needs to have module-droid-card or module-droid-{sink,source} or whatever module loaded beforehand that parses droid configuration and loads the hw module to PulseAudio global object.
Helper binary is separated to its own package, audiosystem-passthrough. When using the helper from PulseAudio if the defaults are not suitable add configuration to PulseAudio sysconfig file. Available options are
AUDIOSYSTEM_PASSTHROUGH_TYPE={qti,af}
AUDIOSYSTEM_PASSTHROUGH_IDX={17,18} # only applicable to af type
Normally just compiling the package against your adaptation should provide working module, but for testing one can also run the helper binary by hand.
In pa configuration disable helper binary for the module,
load-module module-droid-hidl helper=false
Run the helper in standalone mode (type can be either qti or af),
/usr/libexec/audiosystem-passthrough/audiosystem-passthrough -v -a unix:path=.../pulse/dbus-socket -t <type>