Machines of Loving Grace, with Course of Empire and Stabbing Westward, Saturday, February 26, at the Mercury Cafe, is one of those bands that PMRC moms have to listen to several times before figuring out all the lyrics. But even if Tipper Gore wannabes catch the few dirty words on Concentration (this Tuscon band's second album), they'll probably miss the meanings of the real obscenities that vocalist/pessimist Scott Benzel utters. He's slightly less angry than his friend Trent Reznor and not as brash as Al Jourgensen, but he remains disappointed in human nature. Moreover, the Machines' use of aggravating guitars, post-Cold War keyboards and triggered samples creates a perfectly distorted backdrop for Benzel's world-weary observations. The ignorantly blissful had better stay home.