Actually, a hipper take on the basic Muzak idea of instrumental versions of popular music is probably the optimum type of music for use in stores. Vocals tend to polarize listeners into those who like a singer and those who don't. But a piece presented as an instrumental probably won't offend anyone if it's done tastefully. Just replace Muzak's weepy orchestras with competent musicians using instrumentation appropriate to the piece. Or not... I heard s big-band version of Jimi Hendrix's "Third Stone Fom the Sun" a few weeks back that blew me away.