Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Use Sound
CID_SOUND_ONOFF
Parameter: Start Time
CID_SOUND_START
Parameter: Sound
CID_SOUND_NAME
Parameter: Play Sound
CID_SOUND_PLAY
Parameter: Stop Sound
CID_SOUND_STOP