I searched this forum and many others trying to figure out how to keep my factory bose headunit while running a 4 channel and a mono amp. The premium bose was not premium at all to my ears; so, I added a sub and amp. That helped, but the mids and highs were still lack luster. I asked local car audio shops and none could tell me how to do it while keeping my factory HU, but they wanted to sell me the the $300 face plate and a $200 deck. After researching the bose system, I discovered how the amp crossovers all the speakers etc; so, finding a full range signal to send to my 4 channel amp was a problem. I couldn't find any info on the wiring coming from the HU, so I decided to turn the radio on and then start unplugging the 4 or 5 socket plugs from the back of the HU. Bingo, a little 6 wire plug on the left hand side cut the audio when i unplugged it. I proceeded to cut a wire and the left front went out, so I knew that was my left signal. The rest was trial and error, but i figured out the right channel, as well as the polarity. So, this is where I put the Hi/lo converter which I ran to a 1/2 din eq I mounted in my armrest. From the eq i hit the 4 channel amp under my seat (took out the pathetic bose sub) and then my mono amp. After all of this madness I was able to keep my balance, fader (thru the eq) and factory HU and all of it's controls etc. Hope this helps. Peace
