I replaced the CCM in my '03 A6 C5 1.9TDI with one that had the identical part number a couple of months ago and it was completely plug and play. Your key fobs will need to be reprogrammed however, but it's a really quick and straightforward job if you have two. I posted a guide in the C5 forum that explains it step by step. Hope that helps you mate.
Edit
I've just noticed the CCM in your avant ends in an N and the saloon in a K, weirdly the one in my saloon is an N, go figure.