Time for Three appeared, played and conquered a Symphony on the Prairie audience that wouldn't leave without an encore. Violinists Zach DePue and Nicolas Kendall and bassist Ranaan Meyer are in a class of their own, performing a seemingly spontaneous merging of bluegrass, Hungarian gypsy, jazz, country-western, balladry and classical with rambunctious virtuosity. What began in 2003 as an impromptu jam session during a lighting failure at a classical performance in Philadelphia has grown into a brand. Time for Three defies classification -- they simply are. The trio intoned "Amazing Grace," handing off the melody into each other's strings in a moment of introspection. Otherwise, it's boundless energy, beautifully fitted to their newly minted "Ecuador" and other original compositions by Meyer. A clutch of ISO players, playing in traditional standing formation, opened the program with Tchaikovsky's lyrical, dancerly "Serenade in C Major for strings, Op. 48." Having heard the ISO previously deliver this work with gorgeous towering chordal structures, it seemed some sound system technicality must have caused the loss of the luster and distinctive personality expected from the violins.