The MS-8 has gained a poor reputation because it was designed and marketed as a simple solution to great sound. In reality, it is the simple solution to great sound in most systems and tends to work better with simple systems. It basically conflicts with everything that DIYMA is about. For the MS-8 to work its magic, you need to play by its rules (I liken it to using iTunes for that reason). If you play by its rules, it tends to work.
With that said, there is definitely something about BMWs that is does not like - AT ALL. While it can work, it takes a whole lot of effort and trial and error to get correct. Because it is marketed as a processor that can auto-tune, users tend to assume that they don't have to tweak it after-the-fact. That just isn't the case - the EQ is pretty good at fixing calibration issues.