Very sad to learn of this. An LP copy of Pictures at an Exhibition was one of exactly three rock records in my father's otherwise purely classical record collection (Deep Purple's classical mashup and The Nice's Five Bridges Suite being the other two). On very special occasions, he could be persuaded to dig it out and put it on. A friend of my parents leant me a copy of Tarkus, and I dutifully dubbed both albums onto each side of a cassette, which I then played to death as a kid and teenager. Greg's voice was one of the standout elements of ELP for sure.