I don't know who needs to hear this but you can put a JL Audio, 6" W3 in the stock location with a spacer, best run off an external amp though. This subwoofer rocks pretty hard for a 6", it surprised me. My last install before I inherited this 100 Series LC was a BMW 328is, with a IDQ 15" in an infinite baffle install, so I have some points of reference.
Any pics of your 6w3 install?