ok all done, i flipped the crossover around and used the same two bolts, and made sure it sat flat rather than on its side (its a candybar shape inside).. the door went together much easier.
took me 7 hrs! lol.. (plus another 2hrs for the doors) but i was going very slow.. i like to examine the parts to see how they are made, and how each bit goes together... definately don't force anything, so make sure you leave a good part of a day.
you can do the doors first, then the amp second.
i used this guide as mines a E87:
http://www.babybmw.net/viewtopic.php?f=29&t=13605
some tips:
- go slow.. the slower u go the more unlikely you're going to break something.
- get plastic trim removers, very useful, good to wedge between things just to get it started, and the trim remover lever, they are useful for getting clips out stuck in doors
- get a multimeter, easier to see which pair goes to the radio and which pair goes to the sub. for mine they were the same color and size of wires. Sub should measure about 4 ohms.
otherwise its pretty easy, but stay patient, coz i've learnt on previous cars, getting impatient breaks things easily..
one more thing, it was an absolute pleasure working with the trim of this car, everything is quite high quality, and well made. made everything come apart and back together very nicely. (no magic parts lying around)