More info for those who doing it,
3 pairs of RCA going to the boot. front, right and sub from the head unit.
4 pairs of audio cable coming back same way to the ISO connector to plug into te cars speakers connector.
Now the cars connector- its not 4 pairs, its 5 pairs. w220 have a central channel. on the dash next to windscreen ( well at least I never knew it) so one cable sharing ground with fronts I believe, and one sharing ground with rears for the sub.
Thats on the car without Bose from factory. I did swaped original speakers with bose, but Bose simply sucks,
so, after connecting speakers to the amp- front ones died short time after,
so the middbass speaker been replaced with 4 oms ones.
rear for now still bose, but will be replaced soon, as I can hear them clicking on load.
Now rear shelf.
You cannot remove sub without removing rear seats and a rear shelf, I heard of someone cutting peace by peace from the trunk, but thats not human.
so remove rear bench, its got on each side button alike thingy, just push it and the seat is off, then undo 3 screws for the rear back, and you on the shelf.
you need to remove headrests in order to remove the shelf, so-carefully pull-push little black levers next to the headrest holders(plustic pipes there the headrest goes to) to get to them you need to unclip the plastic covers that goes around chrome pipes and pull the headrest away, now I managed to undo only one side of each headrest that way, and then twisted the headrest to the side, and pulled just using brutal force. I pluged them back same way, and they back and working as should.
once you remove all 3- remove the side covers (there the airbag plastic cover) and undo those as well.
thats it, the shelf is yours, remove it- and here we go sub is yours as well.
Now all of it is complicated if you never done it before and dont know how to remove it all. First time I did it- I wasnt sure I can get to it. but then I replaced original sub with the bose one and put it all together-and 2nd time I did it all again, but this time I replaced it with JBL 10 inch sub.
What is the difference. The original nokia sub having 2 connectors, then the Bose have only one, so I connect one connector only, but its not giving any bass, it just plays as a rear speaker. so no point really as the Bose runs the sub from the amp- and then it make sense.
The result was to replace bose with the JBL, and plug in separate amp for the sub.
to get aftermarket sub in there I done some MDF rings, as the cutout in the metal almost 10 inch, and the sub 10 inch, so its like an adapter to house the 10 inch sub in place. I did 3 rings, to get the sub as high as possible so it doesnt stick out much in the boot.
You can use shallow mount sub, then it will stick out way less, or maybe wont at all.
But at this stage its ok with me, as its sticks out 2-3 inches, in the boot space, but I still got plenty of space.
After all this the sound is amazing. its very dynamic sound at all levels, and distortion only comes at very very loud level.
I m not using sub on full power, as the car shaking(from sound) but I m using it just to get me some low frequency not to stress the front speakers much.
I will be adjusting it to my perfection, but mostly its rear speakers, and amps. as I have 2 different brands now, want to have same amps-one 4 channel, one 2 channel, and yes, you can fit them on the rear cover that covers petrol tank, just use small bolts with nuts, and its ok, its quite strong.
So I m hoping this will be usefull to someone, as then I started there wasnt much info on how and that is there.