Have you tried applying the download server behavior to your results page? The server behavior is pretty simple, you tell it where the file is and what file to download and when the trigger occurs it will attempt to download that file from the location specified. Weather the user opens or saves the file will depend on how they have their browser setup, but this will initiate the process.
I would suggest that you add it to a test page first to get an idea of how it works. If you want to include it on your results page you would need to decide how you want things to work first.
If you know the page is secure and you just need that specific file to download you can add the file name as a parameter to the link that the user clicks on, then use this parameter in the download server behavior for the file name. The link might look like this:
<a href="results.php?filename=<the name of the file>">the link</a>
Then in the Download server behavior you would use the lightning bolt icon to set the value for the file name like this:
Please post back with any questions that you have about any part of this.