I didn't really make it clear...the amp is designed to put out its power into a load of around 2 ohms per hcannel.
Most car speakers are 4 ohm drivers and their impedance can reach 16 ohms at times, especially when playing low frequencies, which also sap the most power.
Also, the GS demo car is OUR demo car....L3X JG also had a an IS200 whcih we did a few things to...:)
It had 6s as standard, but I think his is a Premium or something....I don't know much about the individual models mate. :?::D
We have also had experience with the LS400, LS430 and RX300 if anyone was wondering.
Back to what you were saying mate...6s will give you around twice the cone area of a 4"...this is definitely needed, especially for the better response at the bottom 4-5 octaves.
A brighter sound will be achieved by changing tweeters, they deal with the high frequency sound...the fuller sound would be down to the material of the midrange cone and it's breakup characteristics during operation; the standard speakers in 99% of cars are very thin paper cones which will eventually wear out.
Whilst it is good for the cones to be paper, they MUST be reinforced so that distortion is not induced when playing at high levels...this is again caused by cone breakup or flexing during heavy excursion. Unfortunately they must also be LIGHT or the transient response (speed and clarity of reproduction) will suffer.
There is nothing else in your audio system that will affect the overall sound as much as the speakers...they are the most important and critical element fo any install. They should be chosen with care.
Assuming you upgrade to a 6" speaker and you are getting components, i would recommend something like Pioneer TSC series components for a budget of £175, Rockford FNX1514s for around £230 or Digital Designs DDWs for around £350.
For rears I would look at a pair of sub or mid bass drivers in a low Q infinite baffle configuration for around £200.
There really is no need to spend much more than that as the Digital Designs speakers can easily match the sound quality of far more expensive speakers...they really are a bargain.
If you want to read about the DDs you should beable to copy and paste this.
www.termpro.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=13&t=000910
They're rather good mate.
I can help if you need to know what speakers would suit your tastes if you like...I have had a listen to most of the stuff out there.
Chris