The prospect of listening to I Musici, Italy's legendary string ensemble, in the Southern Theatre, Columbus' premiere hall for chamber music, is an experience many local music lovers have been anticipating for months.

The wait was over last night: I Musici -- meaning simply "The Musicians'' -- performed a program that mixed a few esoteric selections with more famous repertoire, in the latter category, chiefly Vivaldi's The Four Seasons.

Formed in Rome in 1952, I Musici has but two remaining founding members, bassist Lucio Buccarella and harpsichordist Maria Teresa Garatti. As new members have replaced retirees or those -- such as Salvatore Accardo -- who went on to other careers, the group has maintained its identity: an ensemble offering high quality, refined interpretations of baroque music played on historically significant instruments.

And how warm and wonderful these instruments sounded in the Southern. One expects the fiddles and cellos to have presence. I Musici's violas and double bass spoke eloquently as well, with an almost palpable resonance produced with, seemingly, a minimum of effort.

The performance was not without its disappointments. The group's concertmaster, Mariana Sirbu, was replaced at the last minute, without explanation, by Gianluca Apostoli. Since the program was not altered, and since it featured the first chair as soloist in two major selections, that substitution proved significant.

The concert opened with a Corelli Concerto Grosso that stylishly announced I Musici's arrival. Lively exchanges between two first violins created an energetic top layer over the ensemble's solid foundation. Two waltzes by Dvorak offered a delectable diversion.

Cellist Vito Paternoster, one of the group's younger members, was featured soloist in Rossini's Une Larme. This highly operatic theme and variations was delivered with enough drama and flair for La Scala.

The gorgeous Handel Passacaglia in an arrangement for violin, viola and strings was where things began to go noticably awry. Apostoli's solos proved no match for the consummate playing of Massimo Paris, who is that rarity: a genuine viola virtuoso (which is not a contradiction in terms, even if hundreds of viola jokes indicate otherwise).

The experience cast a shadow over hopes for the second half.

In fact last night's performance of The Four Seasons -- one of the best-known works in all classical music -- will not go down as among I Musici's finest. The solo violinist must perform with a virtuosity and confidence that were too often lacking in Apostoli's playing.

The mark of a true virtuoso is the ability to make extraordinary things look easy. The performance too often suffered from a sense of unease.

Apostoli brings dynamism and power to I Musici. But his playing last night lacked the elegance and polish that are two hallmarks of this half-century- old musical establishment.