Sō Percussion has commissioned a refreshing new generation of percussion keyboard music. Steve Reich’s Mallet Quartet from 2009 kicked off a subgenre of pieces for two marimbas and two vibraphones. In that vein, fantastic new works by Vijay Iyer, Donnacha Dennehy, and Jason Treuting demonstrate the possibilities of this satisfying combination of wood and metal. Other works combine keyboard instruments with non-pitched instruments such as flower pots (Caroline Shaw), while still others concoct new ways of bowing, striking, and activating the instruments (Elliot Cole).