Celebrating their 40th anniversary, X continue to be a mighty force onstage. Billy Zoom seems to have largely recovered from bladder cancer and continues to dole out his rockabilly-laced licks and punchy guitar chords with casual aplomb. Augmented by guitarist/drummer Craig Packham, the group’s recent concerts have been strong, distinguished by an extended version of “I Must Not Think Bad Thoughts” that sounds even dreamier when anointed with D.J. Bonebrake’s febrile arrangement on vibes. However, it remains frustrating that such great live musicians have been content to funnel their creative ambitions into other projects, releasing no new X material since 1993 and turning into a virtual oldies act. This loaded bill also includes the rootsy ruminations of longtime X collaborator Dave Alvin and the still-jolting Minutemen remakes of bassist Mike Watt, although Alejandro Escovedo is the only artist here still creating exciting new music.