“When you go to heaven and hear singing, it will sound like these three women.” So opined Chris Thile after the Americana trio I’m With Her finished a short yet moving set in the first half of an incredible three hours of music last evening at the Kennedy Center.  The concert hall’s acoustics were ringing all evening as the sold out crowd not only enjoyed the beautiful harmonies from I’m With Her’s Sara Watkins, Sarah Jarosz, and Aoife O’Donovan, but also the instrumental talents and music-making of mandolinist extraordinaire Thile and the Punch Brothers, along with Bela Fleck and Edgar Meyers, virtuosi of the banjo and upright bass respectively. The Kennedy’s Center policy against photography leaves me using old photos from other concerts, but that hardly matters. The music was the focus last evening. Thile was invited to curate a four-day American Acoustic Music Festival, and Friday evening’s show was clearly the headliner.  The Punch Brothers  opened the first half of the show with a tight set capped by the raucous Rye Whiskey.  I’m With Her followed, with …