The civic guys ruined this for us... And it sounds like long weekend BS.
I can't tell you what the law says up here but there must be some reference level that can be used for comparison to determine if you exceed the threshold. I'd find out what, if any, legislation specifies an acceptable db. I'd be surprised to find out you are in violation. Take it to court and have the documentation available supporting that the system is street legal and meets all emissions regulations.
I just bought an M3 which came with a Meistershaft system that seems significantly louder than the AA exhaust in the previously posted clip. To make a long story short, a few weeks ago my neighbour across the street lost control of her car in reverse and creamed my truck in my driveway along with a telephone box and a light standard so I had several officers over. Luckily she missed my less than 24 hours new M3 by millimeters (check out the skidmarks) but I had to move it out of the driveway for the tow truck. One of the officers commented about how great the car sounded!
Keep us updated. I don't get down to the city too often but love the echo off the buildings.