Ok I have bad news for everyone. I've been to my dealer. The answer is :
IF you have a Xdrive M-sport(M-paket) in 18 (style 400M) with staggered(8x18 and 8.5x18) setup 225/45/18 and 255/40/18 summer setup. The ONLY way to put winter tyres and don't have DSC problems (and possibly not ruin bmw warranty on differencials) :
1) To put 225/45/18 and 255/40/18 winter tyres WITH RUNFLATS. I installed non runflats(pirelli sottozeros) in the same setup and DSC is failing. This is due to the fact winter tyres has softer structure and DSC will fail on non runflats.
2) To put squire setup (all tyres are the same) , but you will have to buy 2 additional front wheels to put on the rear 8x18 (as rears are 8.5x18).
So welcome to the world of bmw sales. I actually don't know is it worth to hunt for runflats or buy 2 more wheels , as the tyres size is quite rare and I can't fit other wheels (less than 18") because I have M performance brakes