Mmmk, so I've read the little tuts. about installing a sub in the fit. I actually don't mind the fits stock stereo,well the rear speakers are poo, but up front it doesn't sound to bad. Granted it can't be turned up to much but I'm overly fine with that. So, I'm thinking of getting a sub in the back just cause its always nice to have one

amp - Polk Audio PA400.1 Mono subwoofer amplifier 300 watts RMS x 1 at 2 ohms at Crutchfield.com

sub - Polk Audio db1212 Ported enclosure with one 12" db Series subwoofer at Crutchfield.com

I love polk so its sorta hard for me to get much of anything else, but I've been debating over a type r or some jl, sorta hard to beat that sub+box for $200 though. The sub is ~120 depending where from and teh box seems perty decent and iono..just an assumption is perty much perfect for the sub. The amp, in the cart you get $100 off with 2 polk products/sub+amp so yea, plus it'd compliment the sub almost perfectly. But that's still $180 for the amp.
Anyways, on to the actually situation. If/when I get a sub for the fit, I'm wondering how to wire ti the amp without changing teh stock stereo. My idea is splice into the rear speaker wires at the B...or C? pillar area/pillar between doors and then run the RCA's from there into the amp. But...but new music as R/L bass going on and hearing only the right or left audio would be perty ***. So would I be able to do the exact same thing with RCA's on teh opposite side and bring them together and make one channel..? If I can't would I have to buy that thing that brings 2 channels into one that was used in ummm...well it's someones tut.

edit: hi lo converter in cuteboi's thread

 

get a basslink, built in crossover and an easy install. used the wiring that came with the sub spliced into the read speakers.