How do I use Automator to add files download via Transmission to iTunes? Here's the setup…

Computer A 
- Running Transmission
- placing files in a Dropbox folder
- Uses iTunes Match to load music from Computer B's iTunes library
- Is always running

Computer B
 - Shares Dropbox folder with Computer A
 - Is "master" computer for iTunes Match account
 - Is not always running

Current process
1. Download files via transmission to dropbox folder
2. Start computer B, wait for dropbox folder to synchronize
3. COPY files to "Automatically Added to iTunes folder"

What I want is to have a folder action that when Computer B sees new files in the dropbox folder it will wait till all file transfers are complete, then copy just the new filed into "Automatically added to iTunes"

all of my current tries have caused Automator to re-add all files in the dropbox folder to iTunes, creating duplicates. 

one limitation to be aware of — unaltered versions of the files must stay in the dropbox folder
A couple of solutions come to mind. 


Have your Automator script move the files to the trash (or another folder on dropbox, like "Added to iTunes") after it copies them to the Automatically added folder.  
Set your automator script to check your dropbox for files every x minutes (e.g., 15). Tell it to only copy the files that were added in the last x - 1 minutes (e.g., 14, or 14:59). The Spotlight metadata element you want is kMDItemDateAdded.   
Far and away the easiest solution is to use Hazel.