There are several things which have contributed to classical music in my system. One is the ability of the system to produce not just a wide, but a deep and articulate soundstage. Instrument positions should occupy distinct positions, as they would in a live concert. This is accomplished by a number of factors -- speaker position, room acoustics (including treatments such as diffusion), and a good source and DAC. (Good recordings are, of course, a must.)
The other element which has aided classical music reproduction for me has been having multiple subwoofers. This helps create both the soundstage of a large orchestra as well as the low sounds produced by, say, string bass, timpani, and some of the woodwinds and horns.
Finally, I have been impressed by the ability of some systems -- mine, to a limited degree -- to produce string sections which sound like many individual instruments playing together rather than just a mass of strings. Ribbon or planar tweeters can do this especially well.