In the end I bought the Morels from Comand Online for the front speakers, and they are very good. For the rear speakers I used some Panasonic TS-E171CI just to get rid of the dreadful MB speakers. The rears are not so important for me as I rarely carry back seat passengers. For the centre speaker I used a Faital Pro 3FE22 3 inch 20W/4Ohm
Faital Pro 3FE22 3Inch Speaker Driver 20 W 4 Ohm but make sure you move the capacitor over from the old speaker otherwise the bass will overwhelm it. You need to mod the mounting to get it to fit but the improvement over the standard speaker is night and day. Telephone calls are now loud enough and crystal clear as it uses that speaker but it also improves clarity with vocals on music. Overall the improvement in sound quality over the original speakers is a massive improvement and did nothing to the amps, just using the stock NTG2.5.
The best bit I have done to the car is I soundproofed it in just about every area I could reasonably reach using this as its cheaper than Dynamat
Silent Coat 2mm Mat Bulk The biggest improvement is soundproofing the boot as the plastic tray for the spare wheel is a major contributor to the noise in the car, especially if you have the wider rear wheels (tyre noise). I used some sound deadening mat (Mass Loaded Vinyl) as well as the Silent Coat. Don't ignore the soundproofing, it really helps.
I see you are in London, I am near Saffron Walden in Essex if you want to come and have a listen and see how I installed everything.