I agree with you about that, ie not all models of A4 came from factory with XL - should not be posting that as fact unless they know that your model of A4 did always come with XL from factory.
Using XL were not required, well, maybe common sense should lead you to think that if you are trying to reduce road noise being transmitted into car, then fitting a tyre with a stiffer side wall should always end up with more road noise getting through when compared with its equivalent normal load tyre.
Edit, also, try to keep insurance company happy as in the event of a claim their eyes should mainly be on not making a full pay out - if you fit " not as factory" and have not declared that, then they might just smile and wish you a good day.
Now if I'm wrong and all Avants leave factory with XL tyres, then you must stick with that noise or no noise.