Can I put after market speakers in my 2001 Audi A6?

I have talked with a couple people about this and have gotten different answers. One person told me that i wouldn't be able to put after markets ones in because the factory amp will have problems with them and i have to buy replacement stock ones. The other answer i got (from the service/parts guy at Audi) was that they have never heard of problems with an amp and putting after market speakers in. Please help, can i just go buy speakers and have them installed or are there going to be problems?Can I put after market speakers in my 2001 Audi A6?go have it done at a reputable shop. it can be done