Just to mention, my car has no boom but it doesn't have a thin raspy sound either! It's a deeper sound, more like a V6. It doesn't boom though, it's just right for me. My system is different to yours as the underside of the Brera looks different to the 159.
I've got a feeling my rear silencers are a bit wider/chunkier than yours. This may be down to the Brera having bigger holes in the rear bumper to accomodate silencers. Also, you have a short silencer immediately behind the Vortex - I don't have a silencer there, instead I have a longer silencer tucked in alongside the fuel tank/spare wheel area, in the equivalent position to where your exhaust loops to the left... doesn't look like you could fit a silencer where I've got mine.
Turns out the underside of the 159 is more different to the underside of a Brera than I'd expect.
Brat Pack no.8