I've got an 03 LS with the Touchscreen and THX 6-Disc in dash CD changer. What is the correct cable I need to get Aux-IN for my mp3 player? Every place I got is telling me it is not possible in this car but I thought I read on here that it was.

You mean something like this.

http://www.discountcarstereo.com/detail.aspx?ID=950

http://www.logjamelectronics.com/

what many of us use -> http://www.logjamelectronics.com/auxford.html

Quik is that a good site to order from? Also, which one in particular will work with my setup? I keep hearing none of them will.

I've got a wireless FM transmitter right now and I notice that the volume is crap and it picks up none of the bass from the songs. I literally have to turn the stereo up the entire way just to hear music with 1 window down. Will this adapter eliminate that problem and give me a nice crisp sound?

you need the FRD-03/AUX from PIE

http://www.logjamelectronics.com/piefrd03aux.html

That's the one correct? And can you answer my question on the quality (bass, volume level, etc) compared to the piece of junk FM transmitter I have now.

it taps in through the external cd changer port so SQ is about as good as it gets. Obviously depends on your source material but don't expect any additional degradation.

this will eliminate that this setup from PIE is the best for quality and functionality so you will have nice and crisp sounds.

It connects through the external CD changer port? I thought you unplugged the factory harness and put this in between it?

http://www.thegoodfellas.org/eclipse8.JPG

you do but it "talks" to the radio by simulating an external changer. That's why the button on the radio says CDDJ. The "/s" model "talks" to the radio through the satellite interface.