Hey, How come you don't join them into a Y at the rear where the secondary box used to be? It would help flow a bit wouldn't it? Does it sound the same as the c43s you've done?
I haven't fitted anything yet, but I have bought from Germany a full set of brabus k8 sport cats complete. Just wonder whether they will be better having 4 x 200 cel cats rather than 2x 750 cel standard ones. Anyway they are sitting at home as when I fit them I would like to make a Y pipe before the back box.