It's impossible to say which factor has contributed more to making the Kronos Quartet our preeminent new-music chamber ensemble: the group's effortless virtuosity or its insatiable hunger for fresh challenges. Taped in 1998 (thus reflecting the longstanding Kronos lineup that had held firm until cellist Joan Jeanrenaud departed for personal reasons after the group's 25th anniversary, to be replaced by the equally fine Jennifer Culp), Kronos Quartet: In Accord's many studio performances offer eloquent proof of the group's wide-ranging musicianship, which is equally at home in the cartoon zaniness of John Zorn, the dancing drones of Perotin's Viderunt Omnes, or the slowly unfolded anguish of Alfred Schnittke's Collected Songs..