Just some thoughs...
The first question is, why in the 21st century are you still dependent on a DOS Database program!? 
The second question, is the output to the OS X disk file in Human Readable Format or does it have embedded printer control codes?
The third question is, are you aware that by default additional print jobs are appended to the OS X disk file unless you disconnect/reconnect the Parallel Port and tell it to overwrite?
Your choices are to open the file and manually send it to the printer. You can then delete the contents and save the empty file for the next print job thus not having to disconnect/reconnect the Parallel Port. Or you can create a Service to send the file to a specific printer and this might be able to be incorporated in a Folder Action although I haven looked at that aspect however it can be a Services Context Menu Item.