I am guessing the egg-shell foamed enclosure is for the sound, but you probably have a bunch of sound coming from the fan port, nessisary for ventilation. You can cut a lot of the sound but maintain the airflow by cutting an s-shaped ducting spanning the width of the enclosure. The shape will drop the sound, while then ducting keeps the air flowing. I would not recommend any sorts of filters to block the sound because they are a bit too restrictive for an enclosure in your style.

If my company made a billion dollars while losing 10 billion dollars, I still had a billion dollars in revenue. I just also happened to piss away 9 more billion dollars than I made.