The initial announcements start with weather reports. Accurate weather reports that the NK neither has the manpower nor the computing power to gather and spread along the DMZ. This naturally convinces the NK soldiers to rely on the loudspeakers, if not for news and entertainment, for the weather. After some time, we can literally announce "DPRK soldiers, heavy rain is expected to fall in the evening, so please gather your laundry from the clotheslines" and they will come out of their little posts and start gathering their laundry. This is good rapport. Then come just vanilla news.
Then the loudspeakers broadcast NK news.