Based on some testing yesterday, anyone adding an MS-8 to a BMW E9x who doesn't run a trunk sub, DON'T set it up for the underseats to be subs. Define your system as subless and then define the front as a three-way setup. Otherwise, your 4"s will hate you.
Musicar Certified audio upgrades
OE-Look Enclosures for F10/F30/F32/F22/etc
Add-A-Sub and Full-Bass Packages
Full Cabin 3W and 4W Upgrades
F10 Level Three Add-A-Sub