Get a minidsp (2x4 HD or higher) and use the parametric EQ controls to bring down the highs. If you cannot take measurements just use frequency response graph from published reviews as guide. Treble should not be that much different from room to room so you can use those as reference for where to cut.
I see measurements for RP-600 here https://www.audiosciencereview.com/forum/index.php?threads/klipsch-rp-600m-speaker-review.12138/
Not sure how similar those are to RP-500 but assuming they are seems like a high shelf cut at 2-3 kHz should do it.
I see measurements for RP-600 here https://www.audiosciencereview.com/forum/index.php?threads/klipsch-rp-600m-speaker-review.12138/
Not sure how similar those are to RP-500 but assuming they are seems like a high shelf cut at 2-3 kHz should do it.