In case it helps anyone, I've just fitted my PE and the dealer kindly printed off the 'official' BMW fitting instructions which I've attached.
2.pdf
3.pdf
4.pdf
5.pdf
6.pdf
One tip is not to bother to try to decouple the old exhaust by removing the rubber hangers - they are VERY tight. Instead, just unbolt the hanger brackets, then you can reconnect off the car.
Bear in mind these instructions relate to the European N53 engine (direct petrol injection) which has a much smaller central muffler than some markets and an additional emissions sensor midway along the exhaust. So the centre muffler delete pipework cannot be fitted. In other words it's a rear muffler only.
Overall impressions? Wow! As has been said before, the sound is just great and the rear tips look like an oversized sawn-off shotgun! I shall be driving everywhere with the windows open from now on!
If you've not seen it, this is my favourite PE video clip: