Royal Scottish National Orchestra, Denève, Edinburgh & Glasgow

It's always tough sharing a programme with Berlioz's Symphonie fantastique. Could a promising 21st-century composer and a dream-dance concerto of the early 1930s begin to make the kind of sounds the visionary Frenchman conjured in 1830? Not a chance, especially since Stéphane Denève, who had taken his now fizzing Scots orchestra through Berlioz's explosive masterpiece twice already during their first six seasons together, seemed this weekend to have stripped it down to the classical foundations, worked on every jolt and buffet in the symphony's electrifying string writing and managed to make it sound fresher, if not necessarily more shocking, than ever.

Denève must also take the credit for the enterprising first half of the programme, which worked better in the dry acoustics of Glasgow's Royal Concert Hall on Saturday than it had in Edinburgh's Usher Hall the previous evening (I was lucky enough to hear it in both venues). Edinburgh-trained Helen Grime's Virga was the shortest piece, and by the youngest composer, in his carefully selected Ten Out of 10 series chasing a rainbow of diverse works from this millennium's first decade.

The RSNO's music director came across this concentrated firework, an LSO commission, at the 2009 Proms, and heard in it something out of the usual run of such pieces. My cynical mind was liable to snap shut both at the premise - impressionistic illustration of cloud precipitation - and its opening gesture which, though Grime herself describes it as "striking" in a bizarre programme jumble, struck me only as exactly the kind of woodwind flurry spangled with the usual tuned-percussion splashiness that kicks off a hundred similar exercises.

Curiosity quickly resurfaced, though, as Grime (pictured right) glided via the ghost of a melodic cello phrase from opaque, complicated full-orchestral splatters to curious writing for clarinets and a single first-violin line which may have taken a leaf out of Berlioz's book, almost aspired to that all-important "hook" of an idea which process-obsessed contemporary composers seem so averse to including, and made its mark before the whole thing was quickly over. I admired Virga even more on a second hearing in Glasgow, where the counterpoint could be more clearly balanced and Denève seemed even more intent on bringing expressive warmth. It may not be destined for long-lasting concert-hall life, but Virga has enough in it to suggest that 28-year-old Grime could truly amaze us yet.

But please, annotator Sellen from Cleveland, no more programme-note burble to the effect that "like a cleansing sorbet or astringent pudding, the affect [sic] on our ears (and minds) can be ear-opening and a welcome release from expectations". Your average concertgoer is wiser than you think to that sort of baloney.

There's a hint of waffle, in fact, about Szymanowski's Second Violin Concerto. The promise of its opening hallucination, with violin lines echoed and canoned by wind, piano and muted brass, isn't really fulfilled along lines equal to its iridescent predecessor, nor are its Tatra mountains-style folk dances memorable enough to provide a new kind of contrast. Yet if it's second-rank Eastern European fodder for soloist and orchestra, the ever-questing Frank Peter Zimmermann never played it as if he thought so, and the more scrupulous balances possible in Glasgow brought better co-ordination with dancing side drum than had seemed to be the case in Edinburgh. Zimmermann's Bach encore, too, was much freer on Saturday night, no doubt sensitive to a more intensely hushed audience than the one which seemed to be projecting its restlessness in the Usher Hall.

Even so, by contrast with Glasgow's suitability for Grime and Szymanowski, Edinburgh's plush Victorian venue helped a little more with the upholstery of the strings in the Symphonie fantastique. They've come a very long way since Neeme Järvi started bringing them up to scratch in the early 1980s, and it was obvious from Denève's showcase Proms over the past few years, above all in his Debussy La Mer and a Respighi Pines of Rome covering a vast dynamic range, that he's put in a phenomenal amount of work into shaping the world-class sound they now make. Without which, Berlioz's surprisingly astringent demands would go for nothing.

It wasn't just in the sheer beauty and colour of the flickering violin-and-flute line which etches the idée fixe of Berlioz-as-artist's beloved ideal that the sophistication of the performance first shone through, but also in the unstable, stabbing support, like a heart missing its beats, an effect still as novel as the unpredictable accents of Stravinsky's Rite of Spring. Elsewhere, the supporting harmony we think we hear, which so often isn't there, materialised wraith-like - the aftermath of the shepherds' calls in the "Scène aux champs", poignantly and even desperately voiced by Zoe Kitson's cor anglais and Stéphane Rancourt's offstage oboe - or bent woozily out of shape.

Denève made sure we respected the programme symphony's true credentials - the metamorphoses as well as the mania of the opening dreams and passions, the Beethoven-through-the-looking-glass of the slow movement, here not a note too long - before unleashing the shocks of the symphony's opium-raddled narrator: weird emphatic pizzicati in a March to the Scaffold of unstoppable directness, a witches' sabbath that came almost as a parody-relief compared to the nightmare veils and jaws of a very odd ballroom scene earlier. Yet still the manic pace of the final orgy raised the roof, as it should. And as with all truly novel reinterpretations of the great masterpieces, you went away thinking not so much what a performance, but what a work.

• See what else is on in the rest of the RSNO's 2010-11 season
• Find Stéphane Denève's recordings on Amazon