I do not know much about your exact car but i can tell you this if your intrested in replacing your speakers the best way to go about it is a new head unit new speakers and a 4ch amp. this will allow you a little more versitility and also to be able to get alot better sound quality. I notice that your from the UK and i know there is a real nice company over there called Genesis (
http://www.genesiscaraudio.net/ ) they make real high quality amplifiers. I formerly owned my own 12volt store in the US and that was an amplifier that we had the option to sell it is a bit pricey but the total harmonic distortion is insane crystal clear. as for the speakers get a pair that will require slightly less power than the amplifier can put out so you don't have to drive the amp to it's max potintial this can cause the equipment to break down quicker. Think of it like this if you had to yell all day long by the end of the day after exerting all your force your throat would be sore and you would possibly lose your voice. But if your talking in a normal voice you can talk alday long with very very very little strain on your throat same goes with giving speakers too much power they can take it for a little whil ebut then they start to break down and go bye bye. the bets way to look into speakers is to find 2 or 3 loacal stores talk to the installers and sales people an dlisten to several diffrent brands and find out what you like most i also highly recomend you bring your own CD with you so you know what your music will sound like on those speakers. The head unit you shoul dget is one that i will have 3 sets of RCA pre outs on the back and also easy enough to use that your comfortable with it. Don't get something that you feel over whelmed by in the store cause it looks cool caus eyou will probably pay for features you will never use or kno whow to use. I hope that helps you out. you can feel free to pm me if you would like a little more info.