Sound proofing any suggestions

When I listen to my music I want to be sure that know one else is being disturbed, therefore I am in the process of sound proofing my listening room.Any suggestions as to what will keep the sound from going through the wall which is plaster with two layers of sheet rock that I added hoping it would make a difference. Also since I am into health I am avoiding anything that outgasses therefore no foam or smelly materials. One of my first options are fibergalss the one that is less toxic. thanks
Rip out the drywall and insulate in there. Addressing the finished room,after the fact will suck up the sound--necessitating more volume to overcome the treatment. Oh, and don't expect much control in keeping bass from going thrugh the wall/s.
Avguygeorge has the right idea for it to be done right.A lot of work but it looks like you have done alot all ready. Go to owens corning web site they have the right insulation for sound absorbing and try to leave at least a 1" gap of air between wall + insulation (more is better). you could even use some natural fiber sound deading panells as the wall H/D has them (4' - 8') for around $10.Can.$. If you don't want to rip the walls apart, you could put these panells over the existing wall leaving an 1" air gap. although this might deaden the room somewhat depending on your furnture. But much easier to live'n the room a bit afterwards.
We had good luck using a product called SONOboard in soundproofing a friends bassement. It came in 4 x 8 sheets. It was used in the ceiling and walls which were then finished with suspended acoustic tile, and knotty pine tongue-in-groove. Now even when his amplified band practices down there people two floor up can sleep undisturbed.