Composed for the extraordinarily-gifted Blair McMillen, Toccare! is a study in extremes: explosive, pungent harmonies, lightning-fast scale work, careening from morse code-like tapping in the highest, crystalline registers to “bisbigliando” whispers in the lowest registers, with seething, rhythmic canons rising through the registers. (Rhythmic patterns here are close cousins to those in Magnussen’s ballet, “Psalm” also from 2001.) Tension is always beneath the surface in Toccare!, save for a brief respite in the choral-like section, midway through the work. While rhythmic challenges abound, so do opportunities for lyricism, sometimes pointillistic, other times unabashedly legato.