Basic Audio, er, basics

[UKenGB]

My E53 X5 (Basic Audio, with Nav) here in the UK has no amp, so the radio module speaker outputs must power the speakers directly. Needless to say I want to add amplification to these channels and add a sub (and change the speakers). I know with what kit I'm going to upgrade, but I'm still trying to suss out the stock wiring and hope someone can help (yes I've searched these forums - extensively).

- Where IS the radio module?

I thought it was integrated with the cassette deck behind the nav screen, but...
http://www.xoutpost.com/images/articl...t_Location.jpg
indicates it is in fact in the rear corner by the Nav DVD and CD Changer. So where is it?

- What is the silver coloured box mounted on the side of the mount where the amp would be mounted if it were installed?

This is towards the inside of the car (spare wheel side) and just below floor level and angled down towards the front. There is writing on the side, but it's hard to see and impossible to read. Is this the Radio module?

- What are the dimensions of the amps in the higher grade BMW systems?

I think they reside at an angle, below the CD/DVD decks and I hope to utilise that space, but it would be handy to know the size I have available.

- Am I correct that Sub outputs are only available if a (BMW upgrade) booster amp is installed? So with NO amp in my system, there is no sub signal available?

- Where can I find the speaker cables in that left rear corner so that I can insert my amps. Since I have NO amp there as standard, do the speaker feeds even run through there?

Just trying to understand the standard system layout. Help please.