I wouldn’t waste my money. The standard sound system is very very good and well up to the task!
Interesting. I’ve had loads of BMW’s over the years and always found the standard stereo to be poor. In fact the 5 Series that I sold last year was as perfect as a car could get, and better than any of the hundreds of cars of all makes and models that I have driven over many decades, but the one thing that I kicked myself about was that even though I added £10k of options I didn’t upgrade the sound system and it was still poor! Hopefully when I get to drive one it will have the standard sound system, but they nearly always add Harman Kardon systems to demonstrators and all stereos sound fine in a showroom!