My understanding is the F56 is like the R56 HK system in that the amp controls the frequency that the substandard speakers produce. So...if you are not happy with it, it is very complicated to upgrade.
I have HK and am trying these speakers in the door - Focal IPBMW-S. These cost a small fortune but are designed for the BMW series 1 and 3 that have a similar setup. I've pulled the door trim and scoped the HK mids - They are crappy looking (can't imagine the stock ones!)
I am going to add an amp for the under-seat subs. Not sure how this will sound - but they are clearly underpowered at present.
The long and short of this is buy the stock stereo is you want to upgrade. The HK is too integrated and hard to mod.