When most rock ‘n’ rollers talk about “The King,” they’re referencing Elvis Presley. But for the bands on this 2011 compilation of vintage British prog-rock, “The King” means King Crimson. And though that pioneering group is absent here, Maximum Prog is an awesome collection of rare gems recorded between 1969 and 1975. It kicks off with Don Shinn paying homage to Norwegian composer Edvard Grieg with a groovy, organ-heavy rendition of his “A Minor Explosion.” This isn't nearly as pretentious as it might seem—think of Emerson, Lake & Palmer’s ode to the first movement of Leoš Janáček's Sinfonietta in their “Knife Edge," and you’re halfway there. Aardvark's “Copper Sunset” gets a little more psychedelic, featuring distorted keyboards and fuzz guitar. With ample help from six-string luminary Ray Russell, Rock Workshop infuses an angular version of the old gospel staple “Wade in the Water” with some proto-punk genius that’s softened by gauzy free-jazz brass. Abacus’ “Cappuccino” is most representative of the genre’s penchant to seemingly pull song arrangements from a roll of a 20-sided die.