Have you tried your DAC in a friend's system, one with which you are familiar? That is such a non-fatiguing/non-abrasive DAC, I have to believe that something else is causing your pain.
Have you listened to an all tube-based system? If your ears are that sensitive, you may need to move towards as soft & warm sounding system as possible. Also, have you treated your room? In my room, the harshest tones were always caused by the reflections in the room. As well, the copper speaker cable suggestion is good. Maybe try a pair of Signal Cables. They are excellent and inexpensive.
Oh, and please say hello to the Lion of Flanders if you happen to see him spinning by.
Regards,
Howard