Next week, three prizewinning pianists will play together. It won't be easy, but it should be fun, they tell Arminta Wallace

Pianists don't usually come in threes. Come to think of it, neither do pianos; so a concert which promises three of each, on the same stage on the same evening, also promises a rare treat for concert-goers. Winners' Mozart, at the National Concert Hall, will feature the winners of both the first and the most recent Axa Dublin International Piano Competitions, Antti Siirala and Philippe Cassard, together with competition mastermind and Beethoven Prize-winner John O'Conor, in an all-Mozart programme.

Three calls - one to Siirala in Helsinki, one to Cassard in Paris and one to O'Conor in the US - suggest that these are three very different personalities: Siirala thoughtful and serious, Cassard eloquently expressive, O'Conor's legendary energy barely dented by the experience of having had a concert "snowed off" by savage weather conditions in Cape Cod. So do they have different musical personalities, too? "Definitely," says O'Conor. "But we all have perfectly valid ideas." And as Cassard explains, that's what chamber music is all about.

"It's not egocentric," he says. "It's about listening to the other. You have to share, you have to listen, you have to bring, and you have to give. Then, little by little, you create something amazing. You don't forget your own personality, but you melt it into the others - like an ingredient in a recipe." In this case, with three grand pianos on the menu - not to mention the Orchestra of the Royal Academy of Music under the baton of James Cavanagh - he insists that the resulting dish will not just be suitably dramatic, but also great fun. "The questions and answers between the different players, the games and exchanges: above all, it's fun."

Like all the best fun, it is fraught with pitfalls. "More than one piano at the same time is a difficult combination," says Siirala. "Piano attack is very precise, so if you and your colleague don't quite agree on something, it's very audible. With strings, for example, it's not so transparent because the attack for string instruments is much more imprecise."

So much for two or more pianos - but what about two pianists at one piano? "Well, that's a little bit different. The special challenge in that case is that one of the pianists - usually the bottom one - is using the pedal. When you're playing the top part, you're not used to having to play without pedal. So," - he laughs softly at the idea of it - "they have a great opportunity to sabotage your playing."

As it happens, Siirala will play both top and bottom parts on the night - top in the Andante Con Variazioni with O'Conor, and bottom in a sonata with Cassard. So will there be any sabotage going on? He laughs again. "We'll see."

Cassard, for his part, declares four-hand pianism to be "amazingly tricky". This, he says, is partly down to simple maths. "Because there are two pianists at one piano, your position at the keyboard is not usual. You are too much in the right or too much in the left. Also, you don't see your partner. You sit beside him, but you cannot see him. When you play two pianos, you have your partner in front of you. So you can breathe together. But when you sit beside him - or her - you can't see the movement of the head, of the shoulders, of the face. It's tricky. But exciting."

TRICKY, OF COURSE, is Mozart's middle name. The pianist Artur Schnabel once described the composer's piano sonatas as "too easy for children, too difficult for adults" - a verdict with which most professional pianists, including Siirala, would concur. "I enjoy playing his music very much," he says. "But it's very challenging, and very fragile. The things you need to show from Mozart are often not very obvious. He's one of those composers where you really need to tune in and listen carefully - and then new worlds open up."

For Cassard, the dilemma of Mozart's music is also its greatest strength. "It's not spectacular. It's intimate. And each note is like a diamond. It's easier to play millions of notes by Rachmaninov than five or six notes in one bar of music by Mozart. It's so deep, and you never have one note too many, so the depth of each note is remarkable." But, he adds, the lack of pyrotechnic fireworks doesn't mean a lack of drama. "Every single piece of Mozart's is in fact a little opera. It's really written with scenes, and sets, and changes of lighting, and characters coming on stage and leaving again."

He compares the finale of the two-piano concerto to the finale of The Marriage of Figaro, the slow movement of the F major sonata to a big duet for soprano and mezzo - from Così Fan Tutte, perhaps. "And those two operas, together with Don Giovanni - the Da Ponte texts - contain some of the best music ever written. It's a world. And a bottomless world, you know? It's like Shakespeare. You see everything in those operas. All emotions. An overview of what the human being actually is."

So they wouldn't agree that we're suffering, two months into his 250th anniversary year, from a surfeit of Mozart? "I don't think so," says Siirala. "Even if the occasion is manufactured - I mean, why not the 247th anniversary? - I don't think it's a bad idea to really concentrate on one composer's output once in a while. As long as you can hear other things as well."

For O'Conor, there's simply no such thing as too much Mozart. "There's the variety in the music, for a start - one week you have the piano music, the next the operas, and then you get the string quartets and the symphonies. I don't think Mozart will ever lose his fascination for musicians and music-lovers. In fact I don't think we can ever get enough of him."

If we can't get enough of Mozart, is there such a thing as too many pianos? Absolutely, says O'Conor. "There's a pianist here in the States who delights in doing concerts with eight pianos on stage. But that's a bit of a circus, to be honest. I'm not sure if I'd ever do anything like that."

Cassard, who has already walked a similarly overstrung high-wire act, describes it as "a terrible experience".

"For the 10th anniversary of a big piano festival in France," he recalls, "the promoter commissioned a solo piece for 10 pianos. It was a disaster. First of all, because the piece was very boring, and also because the 10 pianists didn't rehearse properly. So it wasn't together. And then we couldn't see each other - or the audience. And all they could see were our backs, and our necks."

TRYING TO FIT an orchestra around three pianos on stage is, says O'Conor, enough of a physical feat to be going on with - and one which, he is quite sure, will not faze conductor James Cavanagh. "Jimmy is ready for anything. We'll be rehearsing in the Academy, and we're all looking forward to that. It will be fantastic."

As far as preparation goes, he says, though they are in different parts of the world the three pianists have been in constant e-mail contact. "There are a lot of details which can be sorted out that way - what tempo are you doing here? Or, how are you doing this ornament, are you starting from the upper note or on the note? - which in turn saves time at the actual rehearsals."

As far as the "winning" ingredient in the mix is concerned, O'Conor is as aware as anyone that without his early success at the Beethoven Competition in Vienna, his career might never have happened. "In those days," he says, "just to get anybody to take any notice was impossible. It was only when I won in Vienna that they said, 'Oh, well, let's give him a chance'. And here I am 35 years later. Still going."

Siirala, meanwhile, had scooped up all the major prizes in his native Finland by the time he was a teenager, and won the London piano competition when he was 20 before going on to take first prize in both Leeds and Dublin in 2003. Now 26, he is already well established on the international professional scene. Does the concept of "winning" remain important to him as he continuesto forge ahead on the international front?

"Well, he says, "I don't know how you can try to play like a 'winner'. Nowadays almost everybody has some kind of prize in their pocket. But when people come to concerts, they come to listen to the music, and not to hear somebody trying to beat somebody else. For this concert it's nice that we all have prizes. But we will concentrate on Mozart. I promise."

Winners' Mozart is at the NCH on Feb 28