I just did a mini review on a 328i loaner I got without the HK system vs my car with the HK.. Here's the thread
http://www.f30post.com/forums/showthread.php?t=776443
"Harman Kardon vs Standard Stereo:
Is the difference between the two systems worth the extra $$, YES !! They're both very good but the HK system is much better.The standard system sounds tiny compared to the HK system, the bass sounds like one of the woofers is missing. The tweeters were decent but hurt the ears when the volume went up. I wasn't expecting such a big difference, but yea, it's worth the extra money !! The other MAJOR issue is the fact that you can't change the exact frequencies, and are stuck to the general, "Bass" and "Treble", this makes a huge difference on it's own."
Also, I definitely agree that the service department finds excuses for everything. I went in with some rattling and exhaust issues.. They kept the car for 4 days and did f* all. All the ended up doing was the software upgrade. Which doesn't affect the sound system one bit !