Saw your post below re your amp/sub install and removal of the ski pass-through. I was on the point of doing the same thing. A couple of questions?
1) Is your Ci a UK spec car? The reason I ask is that I took out the rear left trunk liner from my 328Ci (non-HK) to check out the amp, but couldn't find one! Do you have a pair of speakers in the front doors (components) and a pair on the rear shelf, or do you have more? Maybe I missed the amp, but I'm positive I checked everywhere, no wires/amp, etc. to be found.
2) I'm planning to do the same thing with the ski pass-through. Does your car have the standard split/fold rear seats? Is it just a case of removing the welds and cutting the seat back carpet? How do you finish the carpet edges in the trunk once cut, and has it increased the road noise (from the trunk now that it's open)?
3) If there is an amp, did you explore getting the factory connector to mate the harness to the replacement amp, or are you happy with these 'piggy back' connectors? Did you get these in the UK?