Are modern sound deadening materials any upgrade for the old stuff, or has the field not really advanced all that far? I've got some dynamat laying around. (Sadly, no CCF or MLV, just the sticky stuff.) If I were to replace the in-cabin-firewall/deck thick mat-thing with that, would I notice an increase in volume?[/QUOTE]
Sound deadening and absorption materials have definitely improved. You can go here and figure out what your needs are or call Nick for advice. Audio guys have proven this is the best stuff going. I have no affiliation....
https://resonixsoundsolutions.com