I have a different approach...since you are using a Denon with DynEQ on, your Surrounds will be boosted by the DynEQ. Lowering them a bit might help with that.
Apart from trying that, there is an easy way to see whether your Speakers just have a fatiguing sound. Of you can, order a pair of Elac UniFi UB5 and use them as Mains. You should be able to order them and send them back if you don't like them. They are pretty much the least fatiguing Speakers I know.
If your problem goes away with those, then it's the Speakers.
I am currently trying the other way, ordered some Klipsch RP Speakers to replace my Elacs because I want more dynamics and efficiency. Once they arrive I will see whether they are OK for me,since I also have sensitive ears...