This is their measurements,(purple for S60) bright on top end and massive 3db dip in mid-range around 1khz, plus smaller, but more significant dip at 3-4khz.
shortly: It's mess. Calling them balanced and neutral is blatant misinformation. You may like their sound signature, but it doesn't make them accurate speakers.
"The S60’s listening-window response (a five-point average of axial and +/–15-degree horizontal and vertical responses) measures +3.16/–1.97 decibels from 200 hertz to 10 kilohertz. "
https://www.soundandvision.com/content/polk-signature-s60-speaker-system-review-test-bench