Hi Bigrich690
Did this exact conversion on my 2005 A4 this weekend with the help of a guide i found on the net, not sure if i got it from this forum or another. PM me with your email address and i will send you it. The whole job took around 3 hours and was fairly easy. The part No for the double din cage you will need is 8E0 858 005 F, don't bother with Ebay as they are only £46 inc VAT from Audi. A new double din climate control unit from Audi is very expensive and the prices for second hand ones are pushing £100 so i cut mine down with a Dremmel, £29.99 from a well known DIY store. It looks perfect, saved a lot of cash and i now have a Dremmel. Only other parts i think you will need along with an RNS-E unit are the leads to convert your existing wiring to the RNS-E, again these are available from Ebay.