Audio system upgrade
But, it is not up to my 2014 E350 Coupe's HK system but the difference is in no way worth spending serious coin to update (IMO)
The most I would do is research the speakers to see if updating them would make the difference worth the effort.
If you are talking thousands sell it and get a W166 with the standard HK audio
I had a 2010 Hyundai Veracruz (Their we want to be like Lexus SUV)
The speakers were all rotted out and the nav display failed, just a huge difference in quality of components






