i you are able to light the floorboard you need to investigate whether there are voids between the floor joists which run through the party wall,

When we moved into our found on garthorne (the red brick kind) I could hear and smell everything from my neighbour when on the landing at the top of the stairs. It turned out that there was a massive hole which I could put my arm through under my boards, between the joists.

When we had our extension done we sound proofed the kitchen/ dining room by doing the following (our architect used to do theatres and concert halls so understands accoustics)

You need to disconnect the wall from the joists. That means removing all floorboards and laying rubber matting over the joists.
You need to install rockwool between the joists in the area on the party wall
You need to then put in a suspended stud wall - you must leave an air gap, putting rubber mat or accoustic padding will do nothing, the air gap creates insulation

We find that the only room where noise is bad is in our bedroom where we can hear our neighbour quite easily, but it isn't bad enough to warant doing the above in this room since we would loose the original cornicing on the party wall in that room, and would cost about £2-3k to do.

Hope this helps