Thanks again to all those that helped in fitting the CD changer to my E430.

Now I have it working I am very disappointed!
The sound quality is abysmal. I now find that there are no facia tweeters on my car, never has been, the holes are still blanked from new!

I also thought that the door speakers were the same size front and rear, but although the rears are the 5.5" that I was expecting the fronts seem much larger. Has anyone any idea on their size, so can order without taking of the door trims to check?

Any suggestions on an upgrade, with about £200/$300 spending limit?

you have the bose speakers or base speakers? i find the bose speakers to be very satisfying.

They are the base speakers

An E430 should have bose speakers, at least in the US.
It makes a HUGE difference b/c Bose speakers have a 2 ohm impedence. I think that is what you have. The Bose front speaker is a 6.5" coaxial. The Tweeter space is only used for the base speakers - go figure.
There a basically no upgrades for the Bose speakers, short of putting in a new amp and installing high quality 4 ohm speakers. Can possibly be done for your price range, probably not worth the effort unless you redo the entire sound system and double or triple your budget.

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2008 S550
2010 GLK350
1997 E420 (retired)
2005 CLK500 (retired)

If it had Bose speakers would there not be an amp in the back next to the CD changer?
There is not one there, so I had assumed that it did not have a Bose system.

It would be behind the trunk cover - on the other side of the trunk lift mechanism. You have to physically remove the cover to tell. Also, "Bose" would be printed on the rear shelf where your speakers are (at least some model years).

__________________
2008 S550
2010 GLK350
1997 E420 (retired)
2005 CLK500 (retired)