Given the rapid, unchecked proliferation of music grads with porkpie hats, jazz-funk might simply be a lost cause. But don't mention this to Swiss pianist Nik Bärtsch. He and his band Ronin retain the genre's characteristic smoothness but do away with many of its excesses (sax solos be damned). Tonight the "zen-funk" troupe offers a minimal alternative to NYC's oft-overblown Downtown scene.