PRINCETON — For the second time in a week, Princeton has been the site of an out-of-town tryout for an important new-music concert in Philadelphia, this time with Orchestra 2001 going deeper into less-charted realms of hybrid theater in a multimedia opera-of-sorts, Slide by Steve Mackey.

It's an ambitious but highly worthwhile undertaking that warranted a trial run prior to Thursday's performance at the Venice Island Performing Arts Center in Manayunk. Though Tuesday's performance at the Taplin Auditorium was a bit cramped, the venue was sympathetically equipped for the piece's audio and video needs — the stage floor looked like a network of cables — and was generally more welcoming than the acoustically questionable Institute for Advanced Study auditorium had been for the Crossing choir's Princeton performances last weekend.

The Slide performance also came with the advantage of having Mackey, Princeton University's faculty composer, both narrating and playing electric guitar, while the librettist, actor/singer Rinde Eckert, played the central role of a jilted, lonely psychiatrist named Renard. The latter is conducting experiments on the nature of cognition and illusion — illustrating how people need their delusions in order to carry on day to day.

The title takes its name from a series of slide-projected photos that intentionally blur their subject matter, first stimulating the imagination of the beholder and then ridiculing it when the photographed object turns out to be something mundane. The Mark DeChiazza projections were mysterious in their murkiness, and the photographs weren't always still. One depiction of animals resembled cave paintings, but animated.

Mostly a single-character drama with incidental commentary from others, Slide tells its story in flashbacks, flash forwards, and engaging digressions: At one point, the question of cognition is examined with the retelling of an episode from The Twilight Zone in which a man thinks he has gone to heaven but discovers he's actually in hell. Less explicitly, Mackey's music is full of unpredictably shifting meters that keep the listener off-guard.

Mostly, Slide is a series of songs, some infused by guitar-based rock but not remotely enslaved by pop song forms. There's the richness of a symphonic movement with the dramatic momentum of an operatic scene. Instrumentation shifted so constantly that the piece was truly on the move even though the dramatic surface is stationary — it's mainly psychiatric brooding.

Where there might be operatic recitatives to set the scenes, Mackey delivered spoken narration punctuated by electric-guitar arpeggios. Though full of theatrical flourishes — and with a big personality like Eckert's, how could there not be plenty? — Slide is a subtle, thoughtfully crafted piece (the pared-down ending is the work of a great composer) that also updates and fuses genres as few pieces do.

Orchestra 2001's informally dressed conductor, Jayce Ogren, had instrumental matters well in hand and played a small, plot-advancing role as a voice coming over an old-fashioned telephone.

As a child of the post-modern performance-art era, Eckert hasn't been about creating a traditional characterization. But he externalizes the inner turmoil of whomever he's playing — whether Renard here or a deranged seaman in the previous Mackey opera Ravenshead — with ironic self-regard and explosive volatility. His penetrating singing voice, freaky falsetto, and idiosyncratic physicality make him a singular presence.

This Slide characterization is more serious and controlled. Eckert projects more of how the character, in a life of deep loneliness, looks to the outside world. But he could go even further. There's greater potential for traditional operatic impact here. And there's nothing wrong with that.

Steve Mackey's "Slide" will be repeated at 7 p.m. Thursday at the Venice Island Performing Arts Center, 7 Lock St., Manayunk. Tickets: $15-35. Information: 267-687-6243 or www.orchestra2001.org