There are several threads on improving the sound quality of the M2.
Here's my post:
https://f87.bimmerpost.com/forums/sh....php?t=1641374
You can swap out the amp with a DSP PNP like the Match UP 7, or replace speakers like I did.
If you love low end base get the Match 7 Amp which has a separate line for a sub in the trunk. Buy your preferred sub and have at it leaving the stock HK subs under the seats. Otherwise there won't be much you can do with the under seat woofers. Its the enclosure that limits is acoustics.
Just changing the fronts speakers and unplugging the center speaker is the least expensive way to open up the sound in the car...
HTH,
HAZMAT