The xx is the exception. The English band’s 2009 debut, xx, is a modern classic, lauded for its moody and sparse pairing of R&B and indie grooves. “Intro,” “Crystalised” and “Islands” all made splashes, and The xx went from 0 to 60 like that. So then comes the follow-up, Coexist, with the words “sophomore slump” […]