I recently did this but with an LC6i instead. Sound improvement was amazzzzinggggg and the clarity is much better along with better bass output because my signal to my amp is now much higher so the amp doesnt have to work as hard to amplify the weak hu signal. As for wiring I run my sub rcas from the rear speaker inputs. I mounted mine under the rear seat cushion.
2 Sundown X10's in 2.5cuft Net tuned to 31.65hz
SKAR SK-1500.1d, SKAR SK-85.4
Lots of Audio Technix 0 gauge
XS Power 1200,XS Power XP3000
I murder lowssss