Two five-star concerts in a row! The Ensemble Music Society has outdone itself, first with the Artemis Quartet a few weeks ago and now with the 10-year-old group of six strings simply called Concertante. Unlike the string quartet, the sextet literature is a bit sparse, but there are always arrangements from other genres to fall back on. For last Wednesday’s program, Concertante didn’t have to; they selected three works conceived from embryo to full born as string sextets: First, Lowell Liebermann’s String Sextet of 2006, a strikingly tonal work for a contemporary one. Violinist Xiao-Dong Wang often carried the melodic line — in B-flat, presenting a pearly tone and an ease of technical command. The work suggests a wistful mood which all the players revealed with consummate precision and matching textures. Brahms’ early String Sextet in B-flat, Op. 18, followed, with slight allusions to Schubert’s last piano sonata (in the same key). The Concertante players revealed more of this work than I’ve previously heard. The evening’s most moving experience, however, was the best performance I’ve heard of Schoenberg’s Verklärte Nacht (Transfigured Night), Op. 4, one of the finest post-Wagnerian pieces to come from anybody. Concertante revealed all its angst-turned-to-joy with ravishing string playing.