Terpene cyclase that catalyzes the cyclization of farnesyl diphosphate (FPP) to delta(6)-protoilludene. (2E,6E)-farnesyl diphosphate = Delta(6)-protoilludene + diphosphate The DDXXD motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family.