For a trimline box set of reissues, this six-CD collection is densely packed with exceptional music, and it's worth exploring for the impressive number of masterpieces it contains. Concentrating here on post-Romantic and early modern music, Daniel Barenboim and the Chicago Symphony Orchestra present key works by Richard Strauss, Gustav Mahler, and Arnold Schoenberg that must be regarded as foundational for the development of 20th century music. The picturesque tone poems by Strauss -- Don Quixote, Don Juan, Till Eulenspiegel, Ein Heldenleben, and the immense Eine Alpensinfonie -- are always regarded among his most spectacular showpieces, and the fact that they take up half of this package shows Barenboim's strong affinity for their masterful orchestral writing, intense expressions, and textural richness. Mahler's Symphony No. 5 and Das Lied von der Erde are among the composer's most profoundly moving and radiant works, and their popularity only grows over time. The final disc brings Schoenberg's highly chromatic and brooding music into focus, covering the lushly tonal Verklärte Nacht and the astringently atonal Five Orchestral Pieces, along with the Six Little Piano Pieces, Op. 19, and the Three Piano Pieces, Op. 11, with Barenboim performing at the piano. The recordings were made between 1990 and 1997, and Teldec's sound is quite good for the period's digital reproduction.