Or if the price of the Remus headers is a bit steep for you talk to Rong on here. He does a Y piece for around £100. You saw the existing pipe off just in front of the seam where the cat is welded in, insert his Y piece and reconnect the standard silencer. It seems to go a bit better, although I doubt if there's more than a few bhp in it, but it sounds nicer too, and not offensively loud. Also supplied with the kit are two sleeves, which when welded to your original cat, mean that you could bolt that back in if ever they introduced emissions testing for bikes. This would doubtless save you rather a lot of dosh if you had to buy a new cat off BuMW having ripped the innards out of the old one. Oh, and just for good measure, it retains all the advantages of the original pipes, i.e. dimensions, balance pipe and Lambda sensors.
As usual, no connection, just a satisfied customer.