the general rule of thumb is to get a calibrated microphone and equalize the speakers to give a flat frequency response .. and if the listening experience remains fatiguing, then new speakers are necessary.
but yes, fatigue can also come from the audio file itself when clarity is messed with.
it could be grainy sounding, but it could also sound like the ringing of your ears .. except instead of a treble sound, the pitch can be adjusted.
again, that pitch can cause fatigue.. and it could be the audio file or it could be the speakers, or it could be the amplifier powering the speakers, or maybe even the DAC providing audio to the amplifier.
i havent heard much difference turning the 'full-range' option on or off .. and as far as i knew, there wasnt any difference.
but if you say you are hearing a difference, that makes me think the fatigue is coming from one of those tiny ringing sounds as if your ears are ringing (but you didnt say what the pitch was).
and if unchecking the box makes the fatigue go away, why not leave it unchecked?
that box should be ment for bass, not treble.. because there are many 2-way speakers that can do all the treble, but not the bass.
i think that whole system of windows doing the full-range thing is to do some bass redirection for when some speakers are bigger or smaller than other ones.
i've always thought the feature of windows stepping in to say something about the audio has been nothing more than a nuisance of annoying & harassment.
but i havent used it fully to note if there is some bass redirection happening for say, when the center channel or rear speakers output less bass than the front speakers (or the subwoofer).
i also havent used it enough to note if the bass gets redirected to the subwoofer when all the other speakers wont output bass.
i will say this..
i didnt hear any difference in the bass when i checked the box, because i think the default is unchecked (or my soundcard drivers uncheck the box when the software installs).
the definition of full-range is really broken.
but the basic term means the speaker will do treble, midrange, and bass all at the same time.
to me.. if the bass stops early, it really isnt full range.. and it gets worse as the limit gets higher and higher.
i think the limit might be defined as 60hz to fit in as full range.