Hi Sezz,
I previously owned a 2.5 N/A MY04 sedan and had the single CD player factory OEM stereo and can't say I noticed any AUX lead or connection at the back of the unit when I removed it to install my aftermarket head unit.
May be some of the others guys here may be able to confirm that for you one way or the other or whether there's some sort or attachment you can get to draw an AUX ?
If you are to install an aftermarket headunit, you first need to purchase a AV Panel Set ( Double DIN ) from a place like japanparts.com so that you can remove the existing factory stereo and aircon control unit and fit the AV Panel set in with your choice if headunit in its place.
You mentioned how or where can you run an AUX cable ? Well, providing your aftermarket headunit has one, there's heaps of place where you can run the cable from behind the dash out to the front. When I had my 2.5, I had a USB cable from the back of my headunit that I routed up into the
centre cubby.
See here for photos of my set up in my previous 2.5 with the AV Panel set and a single DIN headunit. Further in that same thread you'll find photos of my current 3.0R with a double DIN aftermarket headunit.
http://forum.liberty.asn.au/viewtopic.p ... sc&start=0