I don't mind if you want to come over on a weekend, but I'm in Redbridge (east London really) so could be really far for you to travel.
If you have the blacking cards in the front tweeter corner you have got the basic amp, like me.
Here is a link for a bit more discussion about the f11 and speaker upgrade.
http://forum.bmw5.co.uk/topic/84200-...-without-amps/
Also have a look at real OEM, will give you diagram about exactly where the back speakers are. And to buy the top HiFi parts keep an eye on eBay.de as you get far more there than the UK site.