Just to clarify here we might be talking about 2 things:
The M SPORT brakes meaning the standard calipers on an M-sport? Those will clear the regular calipers fine with the 18" Elbrus wheels.
If you're referirng to the M Performance brakes (the upgraded package) I couldn't give you a straight answer.
Does the M performance brake upgrade mandate the 19" wheel upgrade? I didn't think it did, which would lead me to believe you might be OK with the 18's but that's just a theory.
2013 335i M Sport /// Alpine White/Coral Red