Audio Quality of 92' JBL Premium Sound

How much of a difference wil it make if I replace my 1992 JBL Premium Sound System Speakers (2-way 5x7 plate in front, I think 2-way 6x9 in back) with 2003 model, high end aftermarket speakers powered by a seperate 4-channel amp (or 2 2-channel amps whatever)?  I'm driving my interiors right now just off my Kenwood headunit. I don't think it can push them all the way, but that problem would be fixed with an external amp. I know that a lot of cars have been made w/ the JBL Premium Sound, and to be honest my voices still sound better stock w/ my Kenwood than my friend's car with all normal Pioneer speakers.

I know that better can be achieved, cause I've heard people go by with internals like twice as loud as what my JBLs can do. I'm going for loud and clear right now - I've already had suggestions to try brands like MB Quart, CDT, Focal, Diamond, Infinity, Eclipse, Boston Accoustics, Rainbow Audio, Dynaudio, Oz Audio, Brax, Chrystal, Dynavox, ADS, Audax, Vita.................

I know it sounds stupid, but I want to know if anyone has heard a JBL Premium Sound system replaced w/ another aftermarket manufacturer, because right now I'm just assuming I can easily improve my system, but that may not be so and I'm trying not to completely waste my money.

You said you're "driving the interiors just off the kenwood head unit"....so you mean you bypassed the factory jbl amps?

A completely aftermarket system such as the one you are envisioning (4 aftermarket speakers, all powered by the kewnood head unit's built-in amplifier) will normally sound better than most factory premium sound systems.  I think you would notice a definite increase in sound quality if you replace the stock jbl speakers with some aftermarket ones.

If the aftermarket speakers are not installed properly (i.e. factory wiring is used and speakers are accidentally wired out of phase; speakers not making an airtight seal with the rear deck and/or the inside of the doors, etc.) then those could definitely cause the aftermarket equipment to sound like crap.

Thanks for the quick response,

If I get 4 new aftermarket speakers, I'm going to power them off a entirely seperate amp in the trunk for increased SQ and to deliver more power.