Depending on how particular you are you can find speakers that will significantly improve the sound without any alterations. I think Crystalworks has the broadest experience here.

Many years ago I purchased a plug and play set of speakers, amp and subwoofer from Bavsound. I am completely happy with the results. Unfortunately, I don't think they offer a set anymore but it might be worthwhile to give them a call. At the time of my purchase they were extremely helpful.

A couple of years ago I had to replace a tweeter and a local car audio shop had a further upgrade that was also plug and play.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas