By Brandy McDonnellGrammy-winning vocal group Pentatonix, which recently released its fourth holiday album, "Christmas is Here!," returned to NBC this week for its third holiday special, “Pentatonix: A Not So Silent Night.”As previously reported, the special featured the multiplatinum-selling quintet, which includes former University of Oklahoma student Kirstin Maldonado, matching its lovely a cappella harmonies with fellow music stars like Kelly Clarkson, who put the passion into "My Grown Up Christmas List"; Maren Morris, who induced chills on "When You Believe"; and Backstreet Boys, who showed that they know a little about harmonizing, too, with "Winter Wonderland.Read more on NewsOK.com