yah, caraudiosecurity do a ipod kit for 75 bob, seat do it for 99ish. both allow you to control through cd changer controls however you lose use of the changer.
if you want to keep changer, halfords do a kit for 75/80ish i think (have to change track via ipod).
got the same hu/changer, have tried to find a solution to the amp however my findings would suggest a big no no. i have uprated speakers in my doors, tbh it sounds great however if you really want the extra boom your looking at a new h/u fitted. if you find otherwise PLEASE let me know!!
alternatively you can run an amp of the rear speaker cables, get a 3/4 channel amp and use that to run the rear speakers aswell. this has however been rumoured to burn out h/u and amp. i was close to doing it however somany peopele in the know warned me off. your shout. hope this helps