I'm trying to create an app to monitor employee's file attachments using Google's APIs.
I know that I could download all the emails from the audited user list using Mail Audit API and run scripts on the mails but would there be a better way to get sender's email address with attached file names?
Unfortunately, the only options available are the ones you have already suggested.
However, what you can do is to file a feature request on Google's Issue Tracker here and provide all the necessary details about your use-case and what is it that you want to achieve.