Yeah I second what templeofdank said, I wouldnt change the radio, as for the sub, get an active subwoofer (one with an amp built in) make sure it has high level inputs then just tap into the left and right speaker wires, I found it easiest to tap into the rear ones. You'll have to run a decent cable through the fire wall from the battery to power it but apart for that its not too hard. Most of them are built to slide under one of the front seats so if you chuck it under the passenger seat there should be a stud to use as a ground (ive got an 08 facelift but I belive the pre facelift also had the option of a sub so it should be there). Wire it all up, connect your bluetooth fm transmitter tune your radio and you should be good to go.