Your NAV unit HAS AUX INPUT, no need to remove the CD changer.
This thing was posted like a million times on this forum alone.
The NAV unit has both AUDIO and VIDEO input, is just nor wired. All you need to do is add the wires to the connector and you are done. Follow the diagarma below:
Even if you would not have NAV unit, you still don't need to remove the CD changer to add AUX input. There are better ways to get a hard wired AUX input for both BOSE and base sound systems.
The HU needs to come out. There are 3 bolts. One above, and two below. The top one's easy. Just gently pry off the plastic trim above the HU, and it's right there.
For the lower two, you'll have to remove the wooden console trim/shifter bezel.
Apply the parking brake, and place the shifter somewhere in the middle if it's travel. Grab the shift knob, and pull it straight up to remove it (don't whack yourself in the face).
Starting from the rear, gently pry up the wooden shifter bezel. Once it's up, disconnect the connectors for the TCS off button, and heated seat buttons. Once it's off, you'll see the two lower bolts under the HVAC controls.
The HVAC and HU will come out as a single unit, you don't have to separate them to do what you're trying to do.
Are these posts about a super simple matter of removing the HU to access the harness?
You remove the HU and everything is there, exactly like in the picture I provided.
When the car was assembled an assembler connected the harness to the HU, so obviously there is some slack into the cable to be able to put your hand behind and connect/disconnect the harness.
Personally seeing these questions you asked I would recommend you to consult a professional and provide the instruction in this thread.
You will need wires with the correct crimp pins (female) to insert into the 32-pin connector and such.