Installing sub and amp into factory bose help!

Ok so I got an 03 a4 with the bose symphony 2 system. I got a couple subs for free and i want to put one of them into my audi. I got an amp as well and everything but I was wondering how do you go about installing this with the factory woofer? I understand I have to splice the amp and what not into the factory speaker wires because i don't have preamp outputs. But what do i do about the factory woofer? Which wires are they and can i just temporarily disconnect so when i sell the car in the future i can quickly hook it up again? Also are the rest of my speakers connected to the factory amp or is it just the woofer thats connected? I want the factory amp to go to all the speakers and my aftermarket amp to power my sub only. Anyone ever done a sub and amp install in an otherwise factory radio?? ANy advice please!

Hi Hetzner,
I want to do the same on my A4. Have u found any solution ?