The standard head unit only has speaker outputs, no line outs I'm afraid. You can convert speaker to line level with another kit, but you'd probably be better off with a proper head unit in the first place. The double din units and frames are all over eBay, and if you keep the original parts you can always transfer everything to your next car.
There is a well illustrated guide to removing and gaining access to the head unit here:
http://clubjazz.org/forum/index.php?topic=8514.0Sorry to not be more upbeat, but I'd suggest you start with your source material and work down the chain: Bluetooth streaming, DAB, MP3s on SD card etc. > suitable player > amp > then speakers are the final things to buy.
The easiest upgrade on your car is to add the two rear door speakers, as all the OEM head units have four speaker outs.
--
TG