I used a coathanger to fish wires through the stock rubber boot from the door to the A post, and the stock conduits on both sides to run stereo wires.
Pull the kick panels, and you can peel your carpet back, and carefully unclip the spring loaded conduit. There are even cutouts so you can run wires under your seat, and then up along the tunnel if you want. I have mounted an Eman Blue and Profec E-01 this way, and they quite a few extra wires. (I put that stuff under the passenger seat, and then routed the wires up the right side conduit into the ECU via the right lower kick panel.)
Down the left side, I have a 4ga. amp power wire, as well as a few other wires. So there is quite a bit of space if your take your time, and make sure nothing is being pinched. I routed my RCA cables down the middle, to keep them away from power line induced whine and noise.