I'm a little late, but my 2010 and 2011 Maibocks were brewed with S-189. I was pleased with the results. The 2010 version took silver at New York State Fair in July 2010.
Although this does not answer your question of hop substitutions, the 2010 had only Magnums at 60 min. For 2011 I added a little Hallertau at 10 min. This will be brewed again ASAP. Dang, it's already almost half-way thru January!