Buying a WSP b-pipe and HKS muffler,but the maxmods website says the wsp b-pipe only fits to the stock muffler? That mean its not gonna fit on the muffler i'm getting? The muffler has a 2.5 inlet and the b-pipe IS 2.5",so why wouldnt it fit? Also,should I get resonated or no? What's the difference? Thanks.