Well, I have a 2000 ES that is equipped with the stock Pioneer system. I changed out the speakers only (not even the sub yet). Major, major upgrade in sound quality. I purchased Boston Acoustics ES series speakers front and rear. The stock speakers are single cone full range in the rear and use an add on tweeter in front but still use a full range driver in the doors. Result is muddied mid range and harsh, tinny high range. The Boston speakers I put in the rear are coax speakers and component speakers in front. Nice clear and defined high end, very open and much better soundstage. You'll have to change your speakers anyways so why not change them first, it's not very involved and you may not want to change the head unit. I was planning on a double din nav unit but am waffling now because the system sounds so good...