Above link is to my website - and thanks
Yes you can fit a sub to the standard stereo, after reading this post, I put another post on my website about this:
http://www.jamessimpson.co.uk/how-to-fit-a-sub-to-a-standard-stereo
I have just made a video on how to remove the stereo here:
http://www.youtube.com/watch?feature=endscreen&v=VATM7uc6WSA&NR=1
To wire the "High Level Input to Low Level Output" into your car, you will have to tap into the rear speark lines - these are the top two and bottom two most wires (coloured green&green/black and purple&purple/black) that come out of the ISO block:
[img]http://www.jamessimpson.co.uk/wp-content/uploads/2012/04/IMG_0650.jpg[/img]
Hope that helps