The Koni struts in front are also difficult to adjust with the stock front strut-reinforcement bar in place.
If your budget allows, I'd recommend changing to the E82 1M front strut bar, together with the plastic caps that go over the top to keep debris out.
There is also this thread with info about settings for Koni shocks with M-sport springs.
http://www.1addicts.com/forums/showthread.php?t=636984
However in the above thread, the rear shocks are not the koni yellow. They are TC Kline / Koni externally adjustable, such as these
http://www.tcklineracing.com/webdocs...Details943.cfm
I also have TC kline externally adjustable rear shocks. The rear shock body is exactly 1" shorter than the stock 135i shocks. I guess the valving may be slightly firmer, but its hard to be sure.