Most secure method to replicate SQL between firewall

We are installing a SQL database in the Process Network.  This database needs to be accessible from IT.  We do not allow communication from IT network to Process Network directly – a jump through the DMZ is required for security.  Our policy will require a second database in the DMZ.  

Process Network SQL-
The database on the Process Network will send information daily (30-minute to 2 hour increments) to the DMZ SQL database.  This is basically who received how much weight of a certain product for billing. PN SQL dB will also receive updated driver information from DMZ SQL.  This is the Master database.

DMZ SQL-
This needs to have the same information as the Process Network SQL database.  IT personnel will connect to this SQL server to update driver information.  Reports will be sent upstream when data is received from the Process Network SQL database.

The vendor of this SQL software (TopTech) has recommended sending a flat-file via FTP when a value is created/updated in the dB.  My concern here is security and database not being up to date.  Local IT has suggest we open up a port between the two SQL databases for instant replication.

Does Experts-Exchange recommend us to use flat-file via FTP to keep these two databases up-to-date or is a more dynamic approach desirable?  What are the pros/cons of each?  Where does security fall into this?

Thanks,

Donald

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