Complex sentence: From 2006 he competed in the German-based Deutsche Tourenwagen Masters series with Mercedes-Benz, whereas in 2008 and 2009 he dovetailed this with racing in the Speedcar Series.
Split into simpler sentences: From 2006 he has competed in the German-based Deutsche Tourenwagen Masters series with Mercedes-Benz. Since 2008 he has dovetailed this with racing in the Speedcar Series.