before you take the plunge I suggest you check the MC dimensions; IIRC the caliper pistons are a similar (ish) size between shimano disc brakes and magura rim brakes, but the pistons move (in a single lever stroke) >1mm in the latter case and <0.5mm in the former case.
This suggests to me that the MC bore sizes/leverage ratios are completely different; if is is as I suspect, you may end up with ferociously powerful brakes, but that offer stuff-all running clearance at the rim if you use HS33 calipers with shimano MCs.
At least the brake fluid is thought to be compatible though.
cheers