Gerstein, BBC Symphony Chorus and Orchestra, Bychkov, Barbican

What a relief to find Semyon Bychkov back on romantic terra firma after his slow-motion Mozart at the Royal Opera (performances speeded up somewhat, I'm told, after a sticky first night). On his own, dark-earth terms, there's no-one to touch him for nuanced phrasing, strength of purpose and the devoted responsiveness he wins from the BBC Symphony Orchestra - foot-stamping its approval at the end, a rarity - in Tchaikovsky and Rachmaninov.

This week's two concerts in his "Beloved Friend" Tchaikovsky series both hit the heights and plumbed the depths, if not always entirely where expected.

The programming was ambitious and interesting, maybe not ideal in practice. Last night's twinning of death-haunted masterpieces, the Sixth, "Pathétique", Symphony following Rachmaninov's The Bells, might have seemed like a stunning combination as we head towards All Souls' Day; for this listener, the catharsis achieved by the magnificent "Choral Symphony" might have meant slightly less engagement after the interval with its very personal predecessor. Monday's mix of light and dark Tchaikovsky with a rarity, the Oresteia Concert Overture of Tchaikovsky's academic-genius pupil Taneyev, meant a lowering of inspiration; I'd have dropped the Taneyev and substituted for the fitfully interesting torso-movement of the so-called Third Piano Concerto the two amazing movements of the Concert Fantasia.

What I'd give to hear the fabulously clear and weighty sense of fantasy Kirill Gerstein (pictured below by Benjamin Ealovega) brings to Tchaikovsky's piano writing in that quirky structure. He certainly kept the Third's three contrasting ideas on the boil, even Gershwinising the improvisatory-sounding lyrical second theme (An American in Paris seemed to be foreshadowed) and sparkled in an all too short-lived Russian Gopak. But where does that overwrought long cadenza come from in such a context? Bearing in mind that this was the prototype movement for a Sixth Symphony before Tchaikovsky thought wisely and started again - though intriguingly also with bassoon colour at the beginning - the reworking into a fantasia for piano and orchestra deserves a more tailor-made chunk of solo-piano writing.

At any rate Tchaikovsky's fertile imagination still seemed remarkable here, and even more so in Gerstein's magical unfolding of a rarity composed in the last year of Tchaikovsky's life, the Méditation from the Op. 72 set of 18 piano miniatures, alongside the laboured working of a dark "Fate" theme in Taneyev's response to Aeschylus. Only one fragment of orchestral colour stood out: solo violin (Giovanni Guzzo leading on Monday night) against sighing colleagues. And the Furies turn into Eumenides at the Athenian court too soon, namely halfway through the long overture for which Taneyev substituted a shorter prelude. This long peroration is fairly banal stuff, pre-Lloyd Webber placidity, though Bychkov encouraged the BBCSO brass and harps to make it gleam.

The real thing followed, the whirlwind welter of Tchaikovsky's Francesca da Rimini framing what here sounded like the most poignant of all his love sequences, introduced by Richard Hosford's ineffable clarinet. It's certainly the most extended, and the cuts which used to be made in it seemed especially unfathomable when you had such beauties as the cellos giving an especially remote and magical sound to the theme with three-flute adornment. And you had to reel at the sheer depth and sheen of the string sound: principal conductors Jiří Bělohlávek and Sakari Oramo have put in the spade-work on which Bychkov was able to build to make this team sound like the best in London.

Until I heard what Bychkov could do with this searing tragedy at the end of the programme, I'd have been inclined to put the glorious Serenade for Strings in the second half. It can take two approaches: the chamber-orchestral light and bright, perfectly realised in a superb recent disc from the Russian Virtuosi of Europe, and symphonic scope, as here. Bychkov can justify that because of the sheer finesse in the phrasing, the wealth of lovely detail and the gorgeousness extracted from Tchaikovsky's typically amazing engagement of falling and rising scales. The Viennese-style waltz here and its 5/4 counterpart in the "Pathétique" may not have quite leapt balletically, but in true Bychkov style they glided with plenty of subtle rubato along the way.

There was so much to admire in what ought to have been the crowning glory of the series, the performance of the Sixth Symphony last night, that it seems curmudgeonly to admit that if the glitter and thunder of the great march-scherzo had all the adrenalin charge you expect, along with phenomenal detail, this listener remained unmoved. There's nothing to say that the final Adagio lamentoso should come straight on the heels of euphoric frenzy, but all the most shattering performances I've heard have done just that, with conductorly authority from the likes of Neeme Järvi and Vladimir Jurowski able to still the inevitable applause. Bychkov prefers to allow it and then mark a decent silence before plunging into the last rites, but it's harder to accept their world that way.

Besides, all that earthiness is a bit too much in-your-face in the magnifying acoustics of the Barbican, though the sheer brilliance of sound from the trumpets and the thunder of the eight basses duly stunned. Best of all, perhaps, were the wind solos: Hosford again ranging from a reediness that cut through the unstinting fullness of sound Bychkov gets from the rest of the orchestra to the threshold of audibility before the first movement's central cataclysm, and amazing young Amy Harman (pictured right by Kaupo Kikkas), a bassoonist in a million, singing heartache rather than lugubrious gloom right at the start. I don't know by what dint of fortune this ex-Philharmonia player appeared in the BBC Symphony Orchestra, but I hope they can keep her to gild the lily of one of the world's best woodwind departments.

It seems fair to end with a salute to the very best of the evening, Rachmaninov's fine-tuned response to hammy Edgar Allen Poe as refined by the translation of linguistic genius Konstantin Balmont. Perhaps the concert should have ended there, too, since the final move into A flat major light gives us a benediction Tchaikovsky's final moments - rather too rapidly pulsed last night - fail to provide. A performance by this orchestra in this hall - Bychkov's second, and finer - always throws me back emotionally to the last concert of Yevgeny Svetlanov with the BBCSO, two weeks before his death. Only Bychkov can come close for sheer teasing ecstasy in the "Wedding Bells" movement, gilded by a lyric-dramatic soprano in Emily Magee - the conductor's Empress in his magnificent Strauss Die Frau ohne Schatten at the Royal Opera - who kept luminous pitch in the relentless middle-to-upper register vocal line.

Constantly, though, you were thrown back to how both Rachmaninov and Bychkov prioritise the orchestra over the voices, though there was familiar expertise from tenor Vsevolod Grivnov in the opening sleighbell glitter and a superb debut from a handsome young Belarusian bass, Anatoli Sivko, feeling the mournfulness of impending death with heart and soul in the final movement. The BBC Symphony Chorus emphasised open vowel sounds - and open-mouthed keening, not humming, in the outer movements, which sounded wonderful - rather than giving us textural meaning, but that somehow felt right, too. And yes, here I did shed a tear or two as life ebbed away and strings sang the death-rhapsody to its final haven.

• Both concerts to be broadcast by BBC Radio 3 for future broadcast in Afternoon on 3
• Next BBC Symphony Orchestra concert featuring Brett Dean and more Rachmaninov on 1 November
• Read more classical reviews on theartsdesk