If Nico Muhly’s compositions are the busy musical superhighways of your dreams and nightmares, his new organ concerto, Register, started with a whip crack but then seemed to go in reverse.

Yes, as in music played backwards — which was exhilarating, initially disorienting, and slightly mad at its East Coast premiere by the Philadelphia Orchestra on Thursday at the Kimmel Center.

But by the time the music assumed a more typical forward propulsion, your mind was all the more open to Muhly’s alternative mixture of minimalism, dense counterpoint, and post-romantic orchestral muscle.

After his initial shock therapy, Muhly assumed a catch-me-if-you-can exuberance in a piece that, like his Mixed Messages written a few years ago for the Philadelphia Orchestra, is so stuffed with content that numerous hearings are necessary to take in all that the piece is made of.

Unlike much of the modern organ concerto repertoire, this work resists blaring solo flourishes that show off the Kimmel Center’s Fred J. Cooper Memorial Organ — until the closing five minutes or so.

Elsewhere, guest artist James McVinnie had the organ meshing more in the tight-knit ensemble fostered by music director Yannick Nézet-Séguin in a piece that sympathetically cocooned the organ amid all manner of orchestral activity.

What was really being cocooned is an under-the-surface pavane by the Jacobean-era English composer Orlando Gibbons that was sometimes glimpsed, like a still water undercurrent, emerging after the cadenza with yielding, vulnerable music that was hugely endearing.

Not that the rest isn’t likable. Aside from the piece’s oddly inconclusive ending, the concerto seems more like an extremely impressive feat over which one marvels without inviting it into your life.

Tchaikovsky’s Manfred, Symphony in Four Scenes after Byron’s Dramatic Poem, Op. 58, came next — sprawling all over the second half of the concert and amounting to riskier programming. Like Liszt’s Faust Symphony and Berlioz’s Harold in Italy, Manfred has an ambitious extra-musical narrative but is more of an intermittently fascinating white elephant than a neglected masterpiece.

It has so many episodes that the uninitiated ear isn’t always sure where the movement divisions lie. You can try enjoying the washes of sound in the spirit of Rimsky-Korsakov’s Scheherazade, but the music emphatically proclaims greater importance while not always making good on that promise.

For all the composer’s feats of thematic transformation that rival Wagner’s leitmotifs, the ideas aren’t out of Tchaikovsky’s top drawer, forcing performers to invest much of their own personal meaning to make sense of the 50-minute piece’s frequent reiterations.

Though not often played by the Philadelphia Orchestra, the piece received a landmark recording in a 1961 live outing conducted by Constantin Silvestri that was published only in recent years by Pristine Classical.

More than the 2005 performance conducted here by Vladimir Jurowski, Silvestri often treated the piece like chamber music, sometimes downplaying the Philadelphia sound to tell a series of smaller musical stories. This is my preferred approach.

In contrast, Nézet-Séguin was about all things epic, creating the kind of big symphonic picture that’s possible only with an orchestra of Philadelphia’s caliber.

His sense of urgency told you this music is dire in ways that made the satanic fugue of Manfred’s final movement particularly hair-raising. The apotheosis at the end made you grateful for the Kimmel organ — compared to what Silvestri had at the Academy of Music.

Basically, Nézet-Séguin made the music so visceral he left no room for the listener to question it. But as with Muhly’s organ concerto, you were happy to be there, though not eager for more.

CLASSICAL REVIEW

Muhly’s “Register” and Tchaikovsky’s “Manfred”

The Philadelphia Orchestra repeats the program 8 p.m. Saturday, March 16, at the Kimmel Center, 300 S. Broad St. Tickets: $51-153. Information: 215-893-1999 or philorch.org.