Hi, I have also battled this problem since I started this hobby. I have come to the conclusion that it is the "balance" of the sound that affects the musicality/long term listenability of the system. The non-fatiquing systems will force you to turn the volume up higher and higher while the fatiquing systems force you to turn the volume down. So, if the high's are too aggressive compared to a missing bottom end, or midrange, it will be off balance and hence...fatique.
It is very easy for a listener to get fooled by the deep bass, or airy highs.... I have found a balanced non fatiquing sound with my vandersteen 3asig/audio research tube/Linn combination. Yes, one can argue that it is not as "airy" or punchy..etc. But, at the end of the day, I am listening to music more ! I used to have fast, punch sound...guess what, I only used it to impress people and never sat down to listen myself !! good luck.
