running signal wires between head unit and trunk?

[dannysauer]

So, I put a fancy new head unit in a few months ago. That was easy, since I just used it to power the factory speakers. But I got tired of not having a sub, and since the HU has cool built-in crossover stuff and three sets of RCA outs I got a 5-channel amp and a single sub. I finished the box up today (which, now that I've found the forum, I see is almost identical to the "Luke box" - great minds think alike or something). I'm planning to glue some carpet on tomorrow, do the final install of the driver, and drop it in the car. But I thought I'd get some input on how to run the wires back there, since it won't be any fun without a signal.

I figure that a few people here have probably had the interior of these cars apart a hundred times, so someone might have a suggestion on how to best run three 1/4"-ish twisted RCA cables, new front speaker wires, and a remote turn-on lead from the dash to the back. The battery's already in the trunk, and I didn't have premium sound, so no existing speaker wires. I assume there's probably an existing channel or something either under the sills or under the carpet somewhere? And a pass-through to the trunk?

Also, how do these door sills ('89 325i 2-door) come out? I'm used to American cars with a few visible screws - not these "fine automobiles" with fancy hidden fasteners... :)

Thanks for either direct answers or old post links; I can't be the first person to ask, but I'm apparently not trying the right queries to find the answer.

[BMW_TUNER]

Most people run them straight up the middle under the center console. As far as the sills go they are a pita you can pop them all the way off but I usually pop one clip off the rear and slide the trim off and leave the clips on the sill and them slide gym back together.