DIY Car Stereo Auxiliary Input

[screemer11]

So, this weekend I decided to buckle down and finally attempt to add my own auxiliary input to my car stereo, after weeks of telling myself that I wouldn't buy a new stereo under any circumstances.  I ended up, after having much trouble with my first plan, soldering lines directly to the Amp IC inside of the head unit, and ran the lines out of the box.  I took a 3.5mm cable broken out and soldered the right and left channels to the right and left line level ins on the Amp IC and then tested it.  The audio works, however, the sound quality is awful.  And I mean awful.
 
Here's what I'm confused about.  I still have the FM Transmitter and CD player in the car and working, and when the auxiliary input isn't used the quality is fine, and actually exactly the same as before.  So, I know that the problem here is something wrong with my input configuration, not the actual modification that took place.
 
For clarification, my setup involves an iPod Touch 3rd Generation outputting through the 3.5mm jack, going through a standard 3.5 cable split out to the left, right, and ground/shielding.  The ground/shielding is not connected to anything, the left is connected to the left front and left rear while the right is connected to the right front and right rear on the Amp IC.  I then have the stereo set to CD mode with a CD that has an 80 minute track of silence burned to it.
 
Here are some sound clips to show what is going on right now with the system (EDIT: LOOK TO THE BOTTOM OF THE POST FOR HIGHER QUALITY LINKS):
https://drive.google.com/file/d/0B5RwcGf405qYYllMQmtvUnJYM2s/edit?usp=sharing  (Original Track: Passion Pit - Little Secrets:  https://www.youtube.com/watch?v=ScC_pi3PJ9k)
https://drive.google.com/file/d/0B5RwcGf405qYOTdsekRnNGhPLVU/edit?usp=sharing  (Original Track: Of Monsters and Men - Little Talks:  https://www.youtube.com/watch?v=ghb6eDopW8I)
 
Thanks for any help in advance!
 
Edit: I realized that I recorded the original clips in 64kbps, so I rerecorded them at 320kbps.  Whether or not this matters coming from a smartphone microphone is up to you.
Passion Pit - Little Secrets:  https://drive.google.com/file/d/0B5RwcGf405qYbGdzNC1JdExjWTg/edit?usp=sharing
Of Monsters and Men - Little Talks:  https://drive.google.com/file/d/0B5RwcGf405qYTEtoWGNCZVhxUjQ/edit?usp=sharing
 
Edit 2: I also forgot to note that I did not only try my iPod as an input, I tested my laptop and phone's outputs and well.
 
Edit 3: To additionally note, the sound goes out if the ground line broken out from the 3.5mm jack is ever connected to ground, whether through a ground connection on the board or to the head unit/car frame.

 

[screemer11]

Bump

 

[screemer11]

Okay, so for anyone who may be viewing this out of curiosity, I've figured out that the reason for the sound quality drop is a grounding issue with the shielding from the 3.5.  I was able to reproduce the problem by attaching the left and right channels broken out to a pair of speakers I had lying around the house and then holding the ground leads between my hands rather than a direct connection, causing resistance and the same problem that I had before.  However, I'm still confused, as when I connect the shielding to ground in the car the audio goes completely out.
 
Any help regarding this problem would be greatly appreciated.