Sorry, I assumed that you had the Dropbox client installed that synchronised your files to your computer. You can select the folders you want if you only want to download certain folders.
Personally I don't use Dropbox much but OneDrive is capable of having a folder on the PC which is kept in sync with the "cloud" version.
Assuming that Dropbox has a similar client then using that and pointing PlayIt Live at that folder and file seems worth a go.
Your best option is to set up a Monitored Folder on the Dropbox folder which will update the track in PlayIt Live when the file changes in Dropbox.