Yes that's a good point. I think most of the stuff on my iPhoneThe HK system has the potential to be fantastic but choose your sound source wisely.
I've taken delivery of an F56 with the Media XL pack (8.8" screen + visual boost etc.) but not the HK system.
DAB and FM radio sounds okay. Medium quality MP3 (have also tried apple and Microsoft WMA files) again sound okay; high quality digital files sound good for a stock sound system.
Remember the car does not come with a CD player as standard.
Therefore high quality digital sound files will sound better through the car's standard system than your average quality digital files through the HK system.
If you buy the HK system make sure you increase the bit rate of your recordings.