I have a 2004 Audi A8L, and the Cd changer is reading device fault, which means I need to replace....if I replace will I have to do anything to the MMI or is it simply plug and play? and will using burned cds affect the cd changer?

 

I'd have someone look at the CD changer first...I've never had to replace one..usually a temporary jam...fixable.
Burned CD's have no effect on changers, unless you put stick-on labels on them...bad idea...throw off spin and often get CD jammed (or load error) in changer.

 

There are no labels on any of the cds.....

 

Just had this issue with my '04 A8. I thought I would save me some labor costs and just pull out my old changer and put in the new one bought from the dealer. Once done (very easily) I tried playing a CD and got a weird noise fading in and out during the music. Luckily I had put the new one in while sitting in the Audi dealer parking lot. I went in and explained the issue and found out that they had to hook up the car to diagnostics and match the changer to the car. The noise during the music was because the car thought the changer was stolen.