Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Use Sound
CID_SOUND_ONOFFParameter: Start Time
CID_SOUND_STARTParameter: Sound
CID_SOUND_NAMEParameter: Play Sound
CID_SOUND_PLAYParameter: Stop Sound
CID_SOUND_STOP