I listen to about 99% classical music, and very few labels use the rear channels for actual instruments--they just reproduce the hall acoustics, which is the way one experiences live classical and most rock. I don't recall hearing instruments coming from the rear when I saw Jimi Hendrix, Deep Purple, Black Sabbath, etc.! (Never got to see LZ live.) Now, Emerson, Lake, and Palmer did use surround sound when I saw them in '74, but that's a rare exception. For the record, I can hardly stand 2.0 for classical music these days.
DALI Epicon 2 front speakers; DALI Epicon Vokal center speaker; Definitive Technology ProMonitor 1000 surrounds; SVS SB 13 Ultra subwoofer; Marantz AV 8801 pre/pro; Parasound Halo A51 power amp; Esoteric K-03 SACD player; Oppo BDP 105 SACD/Blu-ray player; Sennheiser HD 800 headphones; Woo Audio WA6 headphone amp.