I’m waiting for that very system to arrive as we speak ordered a week ago so let’s hope they got it sent out lol. Unfortunately you can’t buy the down pipe and centre section separate.
I’m not sure if the pipe work is any larger than standard either, I’m guessing not from the photos I just sold my 200 cell cat, if the front one doesn’t do it’s job mail order mot it is lol Or maybe try lean it out with the det3 but I haven’t wired it in yet