A five-year absence in U.S. touring can be a death blow to any musician, even if he is a certified star in his Australian homeland. Yet here’s Xavier Rudd, back with a new band, new sound and plenty of excitement over his latest album “Koonyum Sun.” Not only has the absence not damaged Rudd’s fan base, as evidenced by their buzz on fan boards, MySpace and elsewhere, it’s allowed him to reinvent himself musically. Gone is the heavy, occasionally lumbering, sounds of the music on “Dark Shades of Blue,” replaced with a sprightly, spiritual sound.