I have both the 940 and the 598.
1. Yes. For sure. 940 has superbly extended treble, though you might find it a tad hot. Definitely class above 598's treble.
2. Kind of.... I won't say 940 has a wider stage, but they surely have a fairly wide sound stage.
3. Yes. It beats the 598 in terms of all technical elements, maybe excluding sound stage. Much better clarity, detail, and treble extension.