Ariel Posen’s music occupies the space between genres. It’s a rootsy sound that nods to his influences — heartland rock & roll, electrified Americana, blue-eyed soul, R&B, Beatles-inspired pop — while still moving forward, pushing Posen into territory that’s uniquely his own. He turns a new corner with Headway, a solo album that finds the songwriter taking stock of his personal and musical progress.