Where does fatique come from?

Yes, direct sound to the listening position is certainly not too good. With the drivers directed away from the listening position especially the tweeters, the ears will not be subjected to direct sound that may cause fatigue. One may also be able to crank up the volume higher without hurting the ear-drums with some proper speaker placement especially with minimum toe-in. In this sense, I suppose that omni-directional speakers may hold an advantage although I have no experience with Ohm Walsh designs.

BTW, this is an excellent question. The best way to a pleasant listening experience is to eliminate or minimize factors that cause fatigue. It is something that is not discussed as often as are things like tubes versus SS, vinyl versus digital, detail, imaging, etc.

I am with Mapman and Ryder's rationale. Simply excessive energy in upper mids and lower highs in general. But it could be the entire midrange, if excessive. You would want as flat as possible in the mids and lower highs, then roll off is preferable in highs. Find a component in your system that is the culprit. It could be speakers, source or preamp or even cables. Look to the room in the end unless it obviously has overtly exposed reflective areas. In any case make your evaluation in near field listening to rule the room out. For now.

Recordings can also be to blame. Some stuff on my system just makes me want to get up and turn it off, Sarah McLachlan, "Surfacing" comes to mind. I like her stuff, but this CD just sounds harsh. Then there is stuff I can just listen to for hours.

Long rambling posts ...