When listening to a full orchestra symphony finale, most systems present a wall of sound that is a bit garbled. In a concert hall, you hear all the instruments together, but not mixed. For me , resolving is the ability of a system to get close to that. To unscramble the signal and make individual instruments unaffected by the others. This also has a lot to do with the recording. Only in the last 10 15 years do you have high res recordings who have this detail. And very good systems will show it. Those systems will also reveal any distortion. This is why resolving is a double edge sword. Finally, the type of music is relevant in this issue also: old rock and pop are highly compressed and the garble cannot be undone. But in recent classical, jazz, ambient, folk, solving the equation with high detail makes music sound closer to the real thing. Try Mahler symphony no 3 first movement with Michael Tilson Thomas and San Francisco Orchestra, the last 3 minutes. If you can hear each instrument group clearly, you have a resolving system. If you can hear each instrument separately, you are not human.
