Shipping cars from USA (Luxembourg)

Hey Folks,
Has anyone shipped cars to Lux from USA or any other country? We have two cars Audi A Protected content at around Protected content and Audi A6, Protected content at around 9,000 euros if we sell them in US. They are in a very good condition because we've owned them since brand new. Both run on gasoline, not diesel. Shipping them would cost us about 2, Protected content euros. Is it worth it? How much is it to clear customs? Do they need to be retrofitted to European standards? If yes, how much does that cost?
Thanks for your help in advance!