Personal preference thing, but I don't like the sound of most of Clarion's range. Why did he say you needed new speakers?
Also, why do you want to put speakers in your back doors? Your car never had them from factory, did it? IMO all you need in your car is a set of good speakers up the front and a sub. More speakers just gives you a slightly louder system, definitely not a better sounding system.
If you mix and match different brands and models of speaker you'll get a weird sound too, because of the different response of the different speakers.