Speakers and sizes, again.

[UKenGB]

Sorry to have to return to this oft covered topic, but I've not been able to find the definitive answers.

I have a UK 2005 X5 with what I think is Mk IV Business Navigation, BM53? Does that make sense? I do know what it it and what it does, just not sure of what BMW called it. It has the navigation screen, with cassette behind, DVD Sat Nav and CD changer in the Rear Left. And then there's the speakers, which is where it gets a little fuzzy.

As far as I can determine there's :-
- locations for mids on top of the dash, 2.5" (not known if speakers in there)
- mid woofers in all 4 doors, 6.5"
- tweeters inside door mirror mounts ?"
- definitely no DSP
- no sub
- at this stage not sure if there's any amp in the rear, or if everything is powered from the head unit.

So is this the basic 6 speaker option, with therefore no mids in the dash?
In which case, will there be wiring there for them?
Are above speaker sizes correct?
Am I going to be able to fit JL 6.5" speakers in the doors?
Any chance their 3.5" speaker could be squeezed into the top dash locations?
Do the front doors also have passive crossovers to split signal between mid woofers and tweeters, or are they each fed independently from the amp?

I'm replacing the head unit and installing a decent amp, speakers and sub. I know what needs to be connected, that's not the issue. Just how to interface with existing BMW wiring and other fittings. Obviously much can be determined once I start ripping stuff out, but I want to be fully armed before I start, to minimise down time of the car. So hoping for some answers here first.