My system's high frequencies hurt my ears

FWIW, I think you most often have two choices when setting up bipolar, or a lot of panel speakers. You can emphasize an atmospheric (huge) soundstage or a very detailed or precise type of imaging which might loose a bit of the huge but pick up some precision and a sense of depth of image not otherwise available.

In the first it is all about how you treat the back wave - how it hits and bounces off your walls and to what degree it is attenuated.

The second is determined by how you receive the direct signal, including how it reflects off the side walls, floors and ceilings, as well as how flat the frequency response is, and whether or not it is best heard on or off axis. I've heard very few speakers, but there are some, that sound best on axis. For example, many speaker manufacturers of traditional boxes recommend that the speakers are firing straight forward.

Occasionally, and incident to the rising of a blue moon, you can effectively set up a bi-polar speaker which results in great width, height, and depth of sound stage and have great precision as well. Good luck...........

What I would do in your place to determine what is possible would be to set up your speakers optimally for the precision/tone effect by deadening the back wave and taking that out of the equation. Then you would have a tone you could live with - i.e. no high frequency caused fatigue. After that remove the deadening materials used on your speakers or walls and see how much the back wave really alters your sound stage. You might be surprised (or not). But you could then start to make incremental changes in the surfaces of the rear walls and adjacent side walls to get that huge soundstage effect you are looking for without getting the fatigue back.

In audio as with life, it is all about compromises....

BTW, I agree with the first poster, you have stuff in the signal chain which could certainly help produce the problems you are complaining about. Years ago I solved a similar problem by returning to IC's and speaker cabling that did not emphasize high frequencies as yours might do.

OK my assumption that your listening position was further from the speakers than the speakers are from each other makes my suggestion a bit obtuse. Lets see if this will work, rotate your speaker(s) until the axis is approximately 18 to 20 degrees past your head position. Listen for a while to the new sound (I would do it for some days - just getting used to hearing it). Then then start rotating the speakers back towards your head until the sound improves or deteriorates. When it deteriorates stop and go back the other way by say 50%. And so forth. You should find a sweet spot some where in the range.

Also, since the rear of your speaker is now likely pointed at the side wall/corner behind the speaker, you could temporarily hang a heavy blanket on the wall to see if deadening some the speaker's back tweeter will be beneficial to you. Or if that is not possible, you might try hanging a blanket or two on the wall behind the speakers helps at all. This is all trial and error stuff but if you find a real improvement you can always find domestic materials from bookcases with books, drapes, plants etc which will serve nearly as well as high end and ugly acoustic materials.

This is a slow process but can really be worthwhile.

Try toeing the speakers in until the axis of the speaker crosses well in front of your head. Some of the excess highs might be from the first reflections from the side walls. This will also change the back wave quite a bit and could lower high frequency energy off the back wall as the sound waves have to travel further to reach you.

FWIW, it is not a straight forward speaker issue no matter how logical that may seem due to metal tweeters reputation. I have had similar problems with silk domes etc. Spend a lot of time positioning and repositioning your speakers before you decide to replace them. That is, at least the cheapest alternative. You might also consider trying, as suggested, deadening somewhat the rear wall.

FWIW, going back to your speaker wiring and I/C's. Nordost gets a lot of sales based on how it presents the high frequencies. Great clarity, at least so it seems. For a while. But what I think occurs is that the highs are not in balance with the mids and lows making the sound appear bright. I worshipped mine for about 3 months. Try a cheap experiment - get some Canare 4S11 Star Quad speaker cable and some Blue Jeans I/C's and use them as a benchmark for other brands - they are really inexpensive and good. They have a large following for just that reason. If after repositioning your speakers and treating the walls behind your speakers and using this wire you still have high frequency problems then perhaps it is time to move on. Unfortunately, as you may find out as many others have, this may not be a solution to your problem and that is why I emphasize further exploration with what you have.

Without knowing specifically what your set up looks like it is hard to tell when you will have maxed out the toe in but, assuming that you are listening in a traditional triangle set up, or something close to that, take a piece of paper and draw your triangle. Then draw a perpendicular line from the front of the speaker. Then measure the degree of the angle from the front of the speaker to the center of your listening chair. Then draw a line half way between the chair and the perpendicular line. Then measure the distance in degrees from to the 'middle line' to the perpendicular line. You should get something like 22.5 degrees. But, whatever. Now with the axis of your speaker pointed at your head (in the listening chair :-), you can toe your speaker(s) inward up to the degree you measured (i.e. 22.5?). Once you have done this listen for a while and start moving the speakers axis back toward your head, a couple of degrees at a time. For the fun of it I bet you end up with toe in about 15 degrees from your head.

Sorry for the length of this post. I'm sure there was a much easier way of saying this.