"Air, Extension, Resolution" to a limit is must have. This is what makes music Realistic sounding, provided you have good recording and good equipment that reproduces instrument harmonics faithfully. As soon the scale tips towards excessive ( few dbs above ideal falt response), no matter what the music does sound hifi. Analog on usually sounds warm, has 'complete' music information ( the wave form is not truncated like in redbook cd format), but most of the combos, inexpensive to expensive, I have heard tend to be so warm that it is slightly less realistic when upper mid and low highs( not to mention uppe highs) are few dbs lower than flat response. I think analog needs to be slightly tilted up at the upper freq to be complete. And I have heard some combos that has this. If you have evrything, meaning good cd or analog base system that has flat (my definition of flat being 1-1.5 db tilted up at low bass, flat from 125 hz to 4000 hz, 1-1.5 db up from 4000-7000 hz and then 20 db gently down from 7000 hz to 16000 hz) . I have found that this curve yields the most satisfying balance in my system. Of course my system also is dead quite, has good sound stage- L to R, F to B, and contains great to good components with good cables- nothing too expensive. So much so that I do not want to change a thing. At time where I attempted to go up in top of line preamp or top of line Cd player of same make, or have tried to insert expensive cables, It ruins the balance. I admit some of the things my systems does I know it does not sound right at times, but that is very rare and goodthings outweighs these rare occuances. When you get the acoustic guitar, piano, drum kit (watch for that body, highly defined but some what dullness of the high hats), human voice then everything else pretty much falls in place. In summary, My digital based system sounds pretty much analog with realistics upper mids and highs.
So What is my point? My point is that Air, Extension, Resolution are NECESSARY for high end system. But to a RIGHT degree, be it digital based or analog based. That good combination is hard to find and happens with LOT OF LUCK.