My personal experience is that concrete walls and flooring like a basement make for a bass heavy listening experience, but not a concrete floor-only build like a highrise condo. My last 2 listening rooms have been with wood balloon frame construction, with excellent results. I'm not sure isolation stands will help.
It could be the room and speaker placement is bass heavy, making it sound like there's not enough treble. Maybe try fixing the spectral tilt by dialing down the bass and raising the treble a bit to see if that helps.
