Hello racehorse593. I have worked on many Lexus RX adding aftermarket audio equipment. This is what I have found out. all Lexus RX330,350, and 400h models from 2003-2009 all have the same audio setup. They all have a separate amplifier that is mounted in the rear right, just behind the back seat and under the floor board. It is hidden out of the way. So a few interior panels have to be removed to get access to it. The radio sends only signal (no power) to the amp; The amp has internal crossovers that are built into the circuit board: The amp sends different frequencies to each speaker; Since there is no subwoofer in this vehicle the doors are acting like a subwoofer, this is where your bass comes from, If you turn your radio on and put your ear to the front doors you will notice that there are no vocals/ high frequencies coming out only low frequencies, You have to install a high power speaker when replacing the stock one if not you will blow the new speaker, On the dash you will notice two(2) tweeter locations on the A-Pillars,this is where No bass comes out only the vocals (on 2007-2009 RX models you will notice black plastic screens on the bottom of the windshield, this is another speaker location for midrange speakers); The back doors have a full range signal coming from the amp, this is why you see a tweeter and a 6.5" speaker on each door. email me if you have more questions Juan, notwcaraudio101@gmail