Success has clearly -- and literally -- gone to the heads of Flight of the Conchords.

The change was apparent right away at the New Zealand folk-pop comedy duo's second Twin Cities appearance, a sold-out concert Sunday night at Northrop Auditorium, when they took the stage in oversized, box-shaped robot heads. Granted, the silvery noggins were made of cardboard and foil, like something out of an elementary school production of "Lost in Space." But the symbolism was there.

Jumping up to the Northrop from the smaller (and prop-free) Orpheum Theatre in just a year's time, the stars of the über-quirky HBO TV series "Flight of the Conchords" were upfront about now being the big rock stars that their on-screen characters are not.

The robot attire was just the first costume change, for instance (zebra spandex and gold leather pants were dug up for the faux-metal encore of "Demon Woman"). The duo also brought along what it billed as the New Zealand Symphony Orchestra, although it only turned out to be a guy named Virgil who played cello.

"There've been budgetary cutbacks in New Zealand," explained the wackier Conchord, Jemaine Clement.

Meanwhile, his straight-man counterpart, Bret McKenzie, complained like an Axl Rose-size rock star that "one of the band members" was late to practice recently, a setup to "Hurt Feelings."

One thing that was smaller about Sunday's 90-minute performance was the charm level, though just by a tad. The Northrop's more cavernous setting seemed to stifle interaction with the crowd, which generated some of the funnier bits last year. At one point, though, the duo pointed out a certain male heckler and told the crowd to call him "madame" after the show -- and for the rest of his life. No wonder there wasn't any more heckling after that.

Also, while their TV show picked up its comedic stride this year, its musical bits lagged a bit. So instead of "Hip-hopopotamus" and "Robots" from their first album/season, Sunday's concert featured such lesser songs as "We're Both in Love With a Sexy Lady" and "Carol Brown," a bossa-nova ode to being dumped. (Thankfully, Clement and McKenzie still played "Business Time" and "The Most Beautiful Girl in the Room.")

But the best of the new bits were even better than last year, especially the pre-show climax "Sugalumps," for which the duo, um, opened up to the crowd to emphasize the song's subject matter. "Hurt Feelings" was also loaded with subtle hilarity, such as the inclusion of the word "casserole" in a wannabe hip-hop song to rhyme with a certain vulgar word.

And like every big-headed rock star in Bono's shadow, the guys even tried to tackle the world's current hot-button problem by inserting a lyric about the swine flu in "Think About It," a song about tackling the "issues." Their genius line: "Why don't we get those pigs some tissues?"

See FOTC's set list at Chris Riemenschneider • 612-673-4658