It nearly sounds like (to me) that the two 12" woofers aren’t even running.
yeah, that’s a tell-tale sign. What’s happening is you have very long decay times in the mid-treble range due to the size of the room and highly reflective surfaces. As a result your speakers sound unbalanced tonally, plus the distortion-like effects. You can no longer hear details.
It is kind of like watching a movie with the audio out of sync with the video but here the delayed sound is now incoherent with the direct sound, and the more you turn up the volume the more of that delayed sound you’ll hear, especially in the midrange (Fletcher-Munsen curve).
With enough absorbers the details will emerge but so will the bass. That is, you’ll tonally change it so it’s less bright, more bass. Like taking all the veggies out of a stew, all you’ll be left with is the meat.
Alternatively, move the speakers and listening location as far from reflective surfaces as possible. Don’t forget the ceiling and floor as well for absorbers.