Only the base system needs eq correction .
The older logic 7 systems can be coded to the flat hi fi output according to the posts here.
The Base System or stereo is the one that requires correction because apparently it can't be recoded.
The Hi Fi non logic 7 HU output is a flat 5 volt differential signal
it interfaces with most amps that take a balanced signal without
the need for LOCs
To get better tuning a processor can be added but its not
absolutely needed on a Hi Fi system.
http://www.e90post.com/forums/showthread.php?t=352586
http://www.e90post.com/forums/attach...2&d=1266451970
http://www.e90post.com/forums/attach...2&d=1260829447
For one stop shopping and known working solutions visit
these guys.
http://www.musicarnw.com/bmw-upgrades/