I recently lined the case of my Marantz CD-67SE with Dynamat and had some significant results. I found that I ended up turning the volume down on the powered subs. This surprised me. The sound became a lot richer with emphasis on the vocals. A lot more distinct.
I find it very rewarding to enter into an experimental stage with audio not aware of the end result. There are many additional mods that I can do to this CD player and may that I would not attempt due to the complexity. This was a fast cheap way of improving the sound quality. I have a little left over so I think I will pop the lid on the DVD player and thrown it in.