Complex sentence: It is a variation of the classical pipe organ--expanded with many pipes imitative of orchestral instruments, and capabilities for seamlessly increasing and decreasing volume--intended to facilitate the expressive performance of Romantic music and orchestral transcriptions.
Split into simpler sentences: It is a variation of the classical pipe organ--expanded with many pipes imitative of orchestral instruments, and with capabilities for seamlessly increasing and decreasing volume. These expansions are intended to facilitate the expressive performance of Romantic music and orchestral transcriptions.