Pierre, feel your pain.
E90 L7. Tried everything. 1,000 posts @ DIYMA, Andy W direct advice, Kaigoss advice. Yanked the MS8 and went with just new drivers up-front, 4CH amp driving a sealed sub and the under-seats, OEM amp pushing the rest. Tuned stock EQ using RTA. Very nice- FAR superior to anything possible with MS8. Bloated, loose midbass. Low, misplaced image.
If I had to guess, H/K took some pretty steep short-cuts (assumptions in relationships between phase, FR) in the calibration algorithms to make it work with a slow/cheap processor, but it can't handle the underseat midbass location and that alone effectively messes up the entire auto EQ. Andy admitted issue and said he would do something for me but never did. Dumped it on ebay for a $$ hit of several hundred.
Don't listen to folks who think it needs just one more gerry-rigged calibration run. It will never sound great. Dump it and move on. One thing: get a matching coax center speaker- makes a VERY big difference. FYI: I'm a certified former professional A/V designer/installer.