I too wanted to keep my factory cd player w/ XM. I also have Bose and just wanted to add more bass to it (until I upgrade the whole system sometime soon).
My Setup: I have 2 Kicker 8" L7's in a down-firing box pushed by a Kicker DX700 mono amp that's fed from a Peripheral SVEN2 LOC (line output converter) that's hooked to my factory Bose stereo. Works great, thumps hard!
Here's how I did mine...
I removed the center console "box" & center cupholder tray.
Just grab the tray and pull up on it (remember to remove all loose change from it or it will go flying - yes I forgot to do this step).
[You do not have to remove the console, but I did so I could get a better idea where the wires where coming out from behind the amp] Open the lid to your center console, remove the 4-or-so screws holding on the lid, remove the screws on the perimeter of the center console "box", then remove the 4 screws at the very bottom (underneath the rubber mat). The box should come out after that.
The wires you want to tap in are between the amp & sub. The wires run along the passenger side of the console, look for the blue/white (Left +) and green/black (Left -) wires twisted together.
When I first did this, I tapped into the wires before the amp. The subs were not loud at all. I then switched the wires as I described above, and it was much much louder.
First image, underneath the center console, showing my Peripheral SVEN2 LOC (I used wire-nuts because this is only temporary until I get my EQ put in, it does not affect my sound at all):
Second image, showing which connector to tap into behind the Bose amp:
Third image, showing the Blue/White Wire (+) and Green/Black Wire (-) I tapped into:
I took both Peripheral Negatives and twisted them together with the Green/Black (-), then twisted both Peripheral Positives together with the Blue/White (+). The Black wire you won't use (if you get the Peripheral SVEN2).
I tapped my remote-wire to the back of the radio, I think you can get if from the back of the amp too (pink wire, B11, you may want to test with a test-light to be sure).
