If the members of Koshka are champing at the bit to get their Celtic Connections show onstage at the City Halls on Saturday, there's good reason. The gipsy-jazz trio planned to premiere their collaboration with a chamber orchestra at Celtic Connections 2006 and again last year, but various technical and financial considerations got in the way.

It also took some persuading by the group's violinist, Lev Atlas, and guitarist, Nigel Clark, to get their main composer, violinist Oleg Ponomarev, to consider scoring music for large-scale performance in the first place, and there's an element of good-natured told-you-so in their anticipation of this weekend's concert.

"About four years ago, I found myself thinking about the music Oleg had been writing for the group and it struck me that it had incredible potential for a bigger ensemble," says Atlas, who combines his role in Koshka with the first viola chair in the Orchestra of Scottish Opera.

"I've always had a problem with combining folk music with an orchestra because it doesn't always work, the two styles often don't gel and, to me, it can sometimes become boring or disjointed."

Ponomarev, who first came to the attention in these parts with the phenomenal gipsy music trio Loyko, shared this view. Atlas, however, felt that since his fellow Russian's compositions were drawing on the eastern European school of virtuoso violin playing, they could be orchestrated convincingly to maintain the mobility and emotional content of the trio.

"Unlike the Scottish and Irish traditions, the folk violinists in our part of the world never play as soloists with a guitar or piano accompaniment - they always play in packs," says Atlas. "And that was what made the idea so exciting for me, because it would be violins playing the melodies - only more of them. Oleg was fiercely against this.

"I think his biggest problem was that he felt that he didn't have the experience to score music for an orchestra. But once he thought about it and realised the project's potential and then started producing parts, they worked."

Clark, the guitarist perhaps best known for his work with jazz singer Carol Kidd and the Scottish Guitar Quartet, agrees. "Lev got a friend to look over the scores and there were maybe a few minor adjustments made but technology like the Sibelius computer programme enables you to get a feeling for how the whole thing's going to sound, note-wise at least," he says.

Part of Clark's excitement came from the fact that, even allowing for Sibelius's obvious electronic limitations as to tonal quality, Ponomarev had captured something of one of his own - and Ponomarev's - early inspirations, 1970s jazz/rock fusioneers the Mahavishnu Orchestra. "The three of us get along socially, which helps the music, and the fact that we share tastes in music has obviously been a major factor in the group bonding," says Clark. "In the early days of the group, we were driving through Dublin, where Oleg lives, and he said, You must listen to this', and it was a King Crimson album I'd bought years before.

Oleg's into all that prog rock stuff as well as Mahavishnu; he knows it inside out and you can hear that in the orchestrations."

Ponomarev and Atlas - before he went off into a classical career with the Rostov String Quartet - had rather more difficulty in procuring the music that has come back to inspire them than did Clark. Cue tales of the Russian pair bootlegging albums sneaked into pre-perestroika Russia by copying them on to used X-ray plates - hence the underground expression "music on the ribs". Indeed, so busy did their little industry become that they were almost expelled from the conservatory when their copying factory was discovered.

Such indiscretions are now forgotten: as well as working with Scottish Opera, Atlas is the director of the Russian Cultural Centre in Glasgow, which has given him access to a massive e-mailing list. Through this, interest in - and ticket sales for - Saturday's concert has extended to France, Germany and Belgium.

"It helps that we have a bonus attraction in the Lialia Shishkova Band appearing with us," says Atlas. "This is one of the last of the authentic gipsy groups from Moscow and, as well as being brilliant musicians and singers, they bring a visual element in their traditional dancing, which features an amazing eight-year-old boy."

Having waited three years to hear this expanded project come to fruition, the trio are determined to keep it as an ongoing part of the group's work.

Interest has already been expressed from two orchestras in Dublin: the RTE Orchestra's David Brophy, who conducted Celtic Connections' Brendan Voyage and Altan concert earlier this month, was particularly enthusiastic about the prospect of working with Koshka; and with recent and imminent collaborations between Scottish classical ensembles and musicians, including jazz players Gwilym Simcock and John Patitucci and bluegrass bass virtuoso Edgar Meyers, Atlas feels that the market is opening up for such cross-cultural projects.

"The beauty of this idea, for me, is that it can play at almost any festival," he says. "It's folk music but it would work at a jazz festival and it would fit into a classical event such as Edinburgh International Festival or because of the rock influences in Oleg's arrangements and the energy of the music, it would even sound at home in a rock festival. We'll see what happens but, as a I violinist, I'm so excited about this music because it brings out so many new sounds in my own playing - it really stretches me - and when musicians get enthusiastic about something like this, they want to transfer that enthusiasm to the audience."