My word, but these kids can sing! Sonos represent the innovative edge of nü-acapella, which means members blend the smooth pop-jazz harmonies of Bobby McFerrin with effects pedals, beatboxing that sounds like wan electro-pop, and NPR-friendly new songs, including the group’s own compositions! Four of these December Songs are originals; I don’t expect they’ll storm the X-mas repertoire like John Lennon’s “War is Over”, but they’re not unpleasant if overheard while trimming your tree. Really, though, you could do better. The sextet’s “O Holy Night” is a static arrangement that offers nothing new. “Come Thou Fount of Every Blessing” is an inspired choice, but the polite counterpoint adds little to the hymnal. Sonos scatter some bright ideas here and there, but hasn’t surmounted acapella’s greatest obstacle: how to make the music sound necessary as music, rather than simply as a vehicle for the group’s obvious talents.