I think packing the denser rockwool into a pattern that also disperses (the dense foam absorbs base but reflects highs) we can get both bass trapping and sound dispersion in the most important corners (the article talks extensively about this)
We can then use less dense rock wall and build the typical sound panels.
As for deadening the sound of the room to the outside, that would require a second wall with an air gapped or insulated layer as well as a fake floor, fake ceiling and some sealant around the door.
Basically all of the surfaces would have to have minimum contact to the actual walls floor and ceiling. That seems a bit overkill to me in a room that will only record a few people at a time.
We should focus on acoustic performance. Just my opinion