An orchestra which has been at odds with its music director, to the point that both sides are calling it quits, sounds like a familiar scenario, but in the case of the Philadelphia Orchestra, it is playing itself out presto chango rather than in a protracted battle of wills. Christoph Eschenbach's decision to step down as Philly's music director at the end of next season (after what will have been only five years) was announced last October. The abruptness took many by surprise, though the news - one of the most prominent stories in American orchestral politics of the past year - also seemed, in a way, inevitable. The problem apparently comes down to the all-important but elusive matter of chemistry. Despite the glowing successes Eschenbach has presided over during his short tenure (a new recording contract with the Ondine label after EMI dumped the orchestra in the 1990s, an impressive return to fiscal health), there were reports that a staggering 80 percent of the musicians were out of sorts with Eschenbach's "artistic interpretations." The Philadelphia Inquirer, in its coverage of the tensions between conductor and orchestra, played up the counterpoint of opinions when classical critics David Patrick Stearns and Peter Dobrin (yes, the paper actually has two) wrote side-by-side columns last September on the issue. ("Should he stay or should he go?") As matters have turned out, the Philadelphia Orchestra will be joining a growing number of American ensembles (including the National Symphony and Chicago) nervously casting about for their next music director. But you would have been confounded if you tried to reduce the Philadelphia Orchestra's performance Tuesday night, May 29, to the frame of this troubled back story. It was the penultimate stop on their U.S. spring tour (and first time playing Benaroya Hall in Seattle since their debut there in 2001), and the orchestra attracted what appeared to be a capacity audience. If anything, the affair as a whole suggested a bizarrely bipolar rapport: on one extreme, it was coldly distant, while at the other, blazing and brilliant. Dominating the program's first half was a palpable (if subtle) aloofness. The sole piece here was the Sinfonia concertante in E-flat, K. 297b - alas, not the well-beloved one Mozart wrote for violin and viola but an earlier work of disputed authenticity. Perhaps there's an interesting question lurking somewhere about how perceived authorship skews our perceptions. Still, the Sinfonia concertante is, to my taste, too formulaic and earthbound to excite much interest, regardless of who composed it. The piece is essentially a concerto for four soloists (oboe, clarinet, bassoon, and horn) and orchestra. It's long been commonplace to rhapsodize about the rich string sonority that is considered Philly's signature (though it's a sound that in fact has changed considerably over the years). But one reason behind this otherwise politely pale selection, I imagine, was to showcase such additional strengths as the fabulous winds, and in this regard the performance was a superb success. Four distinct personalities emerged (with especially engaging solo spotlights in the Adagio) but also blended in phrases as intricately interwoven as a Celtic knot. Jennifer Montone's golden horn made an especially memorable impression. The finale, a variations movement, gained much from Richard Woodhams's perky and limber oboe. Eschenbach, dressed in a trademark black Nehru jacket, gave the soloists the kind of flexibility to phrase you'd find from a savvy opera conductor. Yet the rest of the ensemble seemed oddly detached. They played with extraordinary precision and beauty of sound but little warmth. It was as if Eschenbach were driving an impeccably well-oiled machine, while the players were dutifully but dispassionately complying. Compounding the sense of disappointment was the timidity of the programming. How much more exciting it would have been - and a far better opportunity to spotlight the ensemble's excellent principals - to have heard, say, Schoenberg's First Chamber Symphony (which Philly is carrying along in its trunk on this tour, having just performed it in San Francisco). Eschenbach has a well-earned reputation as an advocate for modernist classics and new music. A pity Seattle audiences weren't allowed to encounter that side. Yet all cavils faded away with the concert's second half, featuring Berlioz's Symphonie fantastique. A warhorse, sure enough, but there was absolutely nothing predictable or routine to this performance. Here was a thrilling meeting of minds, with the brightest assets of Eschenbach and orchestra placed center stage and in the best possible light. No matter how well you knew the Berlioz (it strains belief to realize he created this music while still in his 20s), it all became a whirring, dizzying, even shocking hallucination, as if heard for the first time. Eschenbach is unquestionably a brilliant musician - and however much some may critique his interpretive choices, they are the markers of a musical thinker who takes nothing for granted. One of the most compelling aspects of Eschenbach's work at the helm is his ability to sustain large structural arcs while at the same time finessing the most exquisitely telling minutiae. Eschenbach (who conducted the Berlioz sans score) is a master at extracting microclimates, attending to every passing shadow. Take the rippling, nervous rhythms accompanying the idée fixe melody representing the composer's beloved, when it first takes flight. These rhythms rustled with the quality of terrifying obsession. It seemed as if Eschenbach were taking us inside the vision-addled head of the Symphony's hero, making us experience this fixation from within a very unstable individual. The performance indeed came several times close to the edge - one step further and a breakdown into chaos, as in the climax of the Ball movement and several times in the Witches' Sabbath (for example, when the idée fixe turns out not to be so fixed, unraveling in garish, macabre whooping clarinet distortions). Yet the musicians followed willingly and seemed to revel in each challenge hurled their way. I've rarely heard such a variety of piano dynamics or such breathtaking unanimity in a collective diminuendo. And add brass to the litany of strengths along with those fabulous strings - with bells pointed aggressively out, they shook the rafters in the March to the Scaffold and in the final movement. For all the extra-musical associations of the Berlioz (it's become probably the textbook example of Romantic program music), what added to the fascination was sheer exuberance of sonic texture. The wind colors near the end of the "In the Meadows" movement sounded as abstract as a piece of Webern; the harsh metallic bells as the Dies Irae must have prompted a lot of gooseflesh in Benaroya. By the end, there was the sense that a new standard had been set. Why, you had to wonder, would they want to give this relationship up? A brief, head-spinning encore followed: "Dance of the Comedians" from Smetana's The Bartered Bride.