Using this setup, I believe you will end up with three POST requests: two AJAX requests for the Dropzone uploads and a third for your primary form, all of which you will somehow have to piece back together. I do understand that submitting everything in the same request is not ideal, because if you have large file uploads (audio and image files) that fail for some reason, it can hang the browser for quite awhile before giving feedback, which is not a very good user experience.
I would normally create the primary database record first (submitting the main form), then put the Dropzone forms on a second page. That way, you can use your database record's primary key (for example) in the upload URL. This makes it easy to associate the uploaded files with the primary record.