I just finished re-doing the audio in my 2001 Tahoe with "upmarket" factory system- not the Bose system, but the nine speaker system with external amp and subwoofer in the rear left. I made many mis-steps along the way, at times wanting to slit my wrists, so I'm hoping I can save you some trouble along the way. I'm not a professional installer, but I am an engineer with 15+ years of hobby car-audio experience.
- I initially wanted to connect my Ipod to the factory system. I ordered and installed one of the factory adapters (I think from PIE). I was unhappy with the result; it required that the cassette deck was in working order, and actually ran the cassette deck (audibly) while in aux mode. I returned the adapter.
- I installed a new Alpine head unit about a year ago using the Metra wiring harness- kept all other factory components. This worked brilliantly- except that the remote turn-on would not reliably turn on the factory amp (especially when cold, probably due to lower battery voltage). Intensely frustrating.
- My next plan was to replace the door speakers with aftermarket speakers, and route the headunit speaker outputs directly to the door speakers through factory wiring by locating the amp, removing it, and "shorting" the connections. For example directly connecting the Front Left +/- Input wires to the Front Left +/- Output wires at the amp. To access the amp behind the glove box, I had to disassemble the entire center console and dash; even then, the amp was buried so deeply in the dash that there was no way I could work on the Spaghetti-like wiring (20+ wires in the harness). I realized that this was a foolish plan, and that I would have to run new speaker wires directly from the head unit to the doors.
- In the front doors, the rubber boot that runs from the body to the doors is simply a conduit with a large bundle of wires in the middle; there is no molex. After 2 infuriating hours, I figured out the best (only?) way to get the new speaker wires through the boot. There is very little extra space within the boot to pass a thick (doubled over) speaker wire through, it is a tortuous path, and the maneuver requires a lot of force. The solution was to coax a wire coat hanger with a small loop in the end through the boot; use it to pull back a 1 yard piece of 50 lb. monofilament fishing line with a knot at either end; secure the monofilament to a single thickness of speaker wire with duct tape; then use the monofilament to pull the speaker wire through. The first door was torture; the second door took me 10 minutes.
- In the back doors, there is a molex. I followed the simple instructions posted on this site and it took me about 10 minutes per door. I'd like to thank the guy who wrote those instructions; I'd have been screwed without them.
- For the sub amp, I used normal protocol to install a Profile mono sub amp under the back seat. It fit perfectly in the center, and I can still fold the seats down when I need to. I passed the power line and remote turn-on through the grommet behind the gas pedal, and down the drivers' side. I ran the RCA's down the passenger side. No sweat.
- It turns out that the factory sub enclosure is actually pretty nice. It is a sealed enclosure made from injection molded carbon-filled plastic, but it is very heavily built; with a layer or two of Dynamat, it is dead solid. The way it mounts to the vehicle is very nice, and it is totally hidden behind the plastic panel in the rear. I got an 8" Dayton Quattro sub from Parts Express; it has excellent specs at a great price. Turns out that it fits the factory enclosure perfectly, and the volume gives it a near perfect Q=0.7, lightly stuffed with Polyfil. If your goal is to have great sounding audio within the vehicle that is totally hidden, I would strongly consider this option. If you want to rattle the neighbors' windows, build a big ported enclosure.
Summary- trying to do any kind of add-on to the factory system was a disaster in my hands. The factory audio system was a complete nightmare to deal with, but otherwise the Tahoe is a very user-friendly vehicle for audio installs. A complete system re-do (with head unit wired to 4 door speakers, new sub and sub amp) cost me about $500 and only would have taken me 4-5 hours if I had started with that plan in mind. With very modest components (Alpine head unit, Alpine 6.5" coax speakers, Profile 700watt mono sub amp, Dayton Quattro 8" sub) I have an EXCELLENT sounding system, and my truck looks completely factory. This is a nice touch when you live in Memphis; I don't want my truck to scream "steal me".
Good luck!