Keep in mind the OEM CD changer holds 12 disks witch is generally more than you have in the car at any time. Just put the disks in and forget about it, swapping disks is just a matter of selecting 1-2-3-4-5-6 and for the disks 7 to 12 long press on 1-2-3..6 buttons. Is actually more convenient than swapping disks in the in-dash CD player and having disks loose in the car. I again underline how much simpler is to go with the CD changer. Remember Cadillac is not your usual car, that HU plays a roll in the car data line, it also does the clock (display only, the PCM actually has the clock), does the chimes the steering wheel controls, the memory settings, but good luck with your aftermarket.
For those of you who wonder what is the difference between base and BOSE here are some simple diagrams:
Above is the base sound system. Notice how the HU is the actually sound system, you get the power, data, antenna and lights (see on the right of the HU) and out of the HU the sound (already amplified) goes straight to the speakers (i.e. passive speakers). Also notice the E&D data goes to the CD changer (that's how the CD changer communicates with the HU) and also the CD changer audio signal goes back to the HU (as mentioned the HU does everything).
Then you have the BOSE sound system as installed in the '96-'97 Seville/Eldorado (the HU has no in-dash CD for these years though):
Much more complicated than expected. Notice in center the RIM, that IS THE SOUND system. The HU, the CD changer and the speakers are all attached to the RIM. The rim controls the volume level, the BASS, TREBLE, DSP, BALANCE, FADE. Both the HU is just a slave of the RIM. Notice on the right side of the HU you have the same wires as in the base sound system (power, data, antenna, lights). This is why when you plug the BOSE HU in a Base system it does light up it does appears as is working. Note still the HU is the one controlling the CD changer (E&D data line still goes between HU and CD changer) but see the audio wires from both HU and CD changer are going to the RIM. The sound level on these lines is low and constant (NOT VOLUME CONTROLLED). The HU also transmits the chimes to the RIM on a separate mono data line.
As mentioned the RIM does the audio processing, selects the sources based on the signal received from HU on the data line. Then the sound coming out of the RIM although volume controlled (thus not constant level anymore) is still LOW level, the final stage amplification is done by each one of the 4 speakers amplifiers (attached to the speakers). Note that the amplifiers need power to operate so other than sound signal, to each speaker you have power for amplifiers. The amplifier power is controlled by the RIM withe the speakers ON signal that operates the two BOSE relays (left and right) turning ON/OFF the power from the AMP fuse.
I hope by comparing the two diagrams you understand how different is the harness between a BOSE and a base car (the RIM is located in the trunk). This setup is used all the way to 2002 for Eldorado (just that after '98 they have the In Dash CD added to the HU - minor detail).
The third is the BOSE/base setup from the '98+ Sevilles (also 00+ Deville):
This setup is somehow similar with the older BOSE setup but with a difference in the number of speakers and the fact that the RIM now called AMP incorporates the amplifier too, so no more amplifiers on each speakers. Basically what ever comes out of the AMP is speaker level audio signal. They have an additional SUB and some (most) have also the nose cancellation microphone (also attached to the AMP). Still that unit is THE sound system, all the others are attachments.
I did not included the optional cell phone module (later OnStar and Satellite Radio), they all connect to the RIM. Also I did not mentioned anything about the steering wheel controls, well the IPC in the '96-'97 Seville and '96-'02 Eldorado does the A/D translation while in '98+ Seville ('00+ Deville) the DIM does the A/D conversion, then the signal is sent to the HU using the data line. The HU forward the signal to the RIM/AMP for the BOSE cars, this signal is used by the HU just to actuate the display.
Follow
this thread to find out in details about coverting from base to BOSE.