If you are not fully set on the LC6i I would suggest you look into a PAC AmpPro https://pac-audio.com/catalog/amppro...faces/ap4-ch41 It will give you a perfectly clean signal from the radio and retain all the chimes etc. You will also not have to (or have the installer) butcher up your wiring. PAC also has an amplifier T-harness so that you can more easily wire back to the speakers if you want https://pac-audio.com/catalog/audio-...acing/aph-ch01
The AmpPro you can get online for about $260 and the harness for about $35.
As for the loaded enclosures, it just depends. Are you actually trying to place the box in the location that the factory one is under the rear floor or just simply in that area in the rear above where the factory sub is located? With the 8" you may get some more output around where it is tuned to but the 10" can be a bit cleaner sounding, up to your ears.