I want to soundproof my wall. In fact, it's this wall:

I know, right? It would probably be an enormous task, but I really want to get it soundproofed because I have a neighbor on the other side and my entertainment center is right up against the wall. I have no speakers mounted on the wall, so that helps, but I am afraid that the bass from my subwoofer is just tearing through that wall. If you must know, it's a 5.1 system with the two front speakers mounted on stands and placed next to the TV. The center speaker is the one I am mainly concerned about.
If it's too much of a job to insulate such a huge wall, then perhaps there's something i can put between the wall and the entertainment center.
I have heard of foam insulation and mass-loaded vinyl (which I really like the idea of), but just want to hear some tips from the stack folks.
Edit: Is the home improvement forum on StackExchange brand new or something? The word insulate isn't a tag? Neither are condo or townhouse. Could someone with some rep add these?