For its Winter Festival at Benaroya's Nordstrom Recital Hall the Seattle Chamber Music Society has been offering a characteristically interesting mix of chamber music combinations and works. In seven concerts between January 24 and 27, on my count 13 musicians been have performing 20 works by 20 different composers, in 11 different combinations. A number of the works are likely to be new to most listeners - Amy Beach's Quintet for Piano and Strings, and pieces by Cyrille Rose and Libby Larson, for example. What was innovative in the concert of keyboard music on last Saturday was not the choice of pieces; after all, neither Bach's Goldberg Variations nor Rachmaninoff's "Symphonic Dances" suite is a new discovery. What was striking was their inclusion in the same program; it may possibly be the first time they have ever been put together in the same concert. Few people would regard the two composers as natural musical bedfellows. It is by no means every concert promoter who, to follow a performance of the massive Goldberg Variations by one pianist, can pull out a second pianist to join him in the extremely taxing original two-piano version of the Rachmaninoff piece. Nor is it every concert pianist who is comfortable in both styles of composition. In the event it proved a successful combination, enjoyed by a near-capacity audience. Bach's lively and genial masterpiece, with its cheerful and surprising medley of popular songs just before the final re-statement of the theme, contrasted interestingly with the elegiac, wistful, and uneasy tone of this last major composition from the Russian exile in America, with its undertones of violence and fear of death. Of the two performances, the Rachmaninoff was the more successful. Adam Neiman and Jeremy Denk played well together, and their two pianos were better in tune than one sometimes hears in two piano recitals. They caught the work's mixture of dark lyricism and unpredictable, shifting, moods very well, especially in the extraordinary waltz movement where Rachmaninoff turns the classic dance into an ominous, haunted, evocation of a lost world. The performance of the Goldberg Variations made a more mixed impression. There was much to admire in Jeremy Denk's subtle and intense rendering of the theme and the slower quiet variations, and in his virtuosic handling of the extremely demanding fast variations originally written for a harpsichord with two manuals and involving hand-crossing at high speeds which is very hard to bring off on a piano. The overall impression of the performance was, indeed, of virtuosic power; tempi tended to be fast and in one or two of the variations - for example number 28 - the music seemed gabbled instead of flowing. Denk's tendency to hurry from one variation to the next with no pause between them, and the omission of repeats in many of the variations, deprived the audience of the chance to savor in full the distinct character of each. Part of the work's fascination and beauty lies in the variety and contrast that Bach brings to his development of the theme and this did not emerge as strongly as it can. If there is any truth in the legend that the work was commissioned as a diversion from insomnia by Count von Keyserlinck the Russian ambassador to the Saxon court, the Count might have found this performance somewhat lacking in reposeful qualities and beguiling charm.