I've also fitted this aux kit from amazon this week. I've got the RCD500 but they are very similar, just check you have the CD changer port available on the back.
I installed the little grey box that comes with it behind the climate control panel and have run the lead coming out the bottom of the centre console. Only took around 45 mins to do.
Works and sounds really good.
Only other tip you'll need is to be aware that when u take the radio out you take a lot of the centre console apart, and when you unplug the little light that shows if the passenger airbag is off, this will cause an airbag fault to appear if the battery is connected, this will need to be reset after.