You could get a Sports cat like http://www.japspeed....-downpipes.html. if worried about breaking the law lol
Not sure what they are like on zeds but have one on our Scooby, no problems Also, know friendly garage if you go full de-cat.
Edit: Actually not sure what is compatible with the Invidia system...would the Cobra fit? Love the sound of mine Has it been mapped? Will need a re-map???