I'm only dipping my toes into entities now and starting to find my own current limitations (media like yourself, sorting, etc), so I'm not aware of all the potential pitfalls.
My thought though, is that if you were setup your capture form to write the filename of the image and audio to values in your entity list now, eg filename_photo and filename_audio, then you have all the data you need to build your choice list (use the entity OData url to pull and transform your entity list regularly and update your form with a current choice list that has the entries and their filenames)
When media are supported in entities, hopefully there's a simple way to upload/link files to an entity, and your entity list will already have the filenames for matching. Presumably the media support would let you create new entities and directly store these media against the entity in the designated/reserved values for this, eg entity:image1 and entity:audio1 or attachment:image1 etc.
And your followup form would still point at the entity list, but instead of also needing an internal choice list that has each entity ID plus filenames, and uploading media as attachments, it would be modified to get the media from the linked blobs in the entity list.