The term musicality gets used in different ways by different audiophiles, but there is one usage that I find the most informative: A system is described as musical when the sound it produces is perceived by the listener as a GESTALT, rather than a collection of individual elements like resolution, tonal balance, imaging, and so on.
Of course, the likelihood of gestalt perception depends as much on the inclinations of the listener as it does the characteristics of the system. Some people seem naturally inclined to listen analytically, and some systems seem to promote that. Other people seem naturally inclined to listen holistically, and some systems seem to promote that. When a system tends to promote holistic listening, it is often described as musical. And that seems to me to be a useful enough adjective to have around.
