Twin resonator removeal
I am really grateful to this thread for providing support and help for exhaust modifications. As a result of reading this, I had the twin resonators towards the front replaced with straight through piping, and have for the time being left the middle muffler set up and left the stock mufflers. The difference is more burble, slight deeper and meaty sound, and acceleration is noticeably louder but not over the top. Acceleration also seems more free especially on low revs, which is probably due to less back pressure. The exhaust shop said the twin resonators were full of wire wool, which pushed the exhaust into the sides of the resonators and around, which must have caused slowing of the exhaust gases. Exhaust shop BMW expert said that this is now how the car should sound.
So to help with the general information on this thread and to add to the 'database' of sounds, I have uploaded a video of before and after - I have to say though the video does not do a huge amount of justice to the difference, but in real life it is more noticeable. Without the top down, the sound with modest acceleration is nicely louder than stock, and with the top down, much more noticeable, even when just sitting in traffic.
Hope this helps.