That's a classic symptom of too live of a room. Whatever you can do to absorb some higher frequencies would help. Carpet, drapes, artistic acoustic panels, etc. are what will help most.
Suggested upgrade paths
So, I am looking at spending 5k to improve the sound of my very modest system. I currently have a Rotel 1592. Being fed by an Eversolo DMP A6. I’m using the Rotel DAC, as I didn’t like the ESS DAC. This feeds a pair of Wharfedale Super Lintons.
While it sounds ok with the volume at 60-65. If I want it louder, the treble is shrill to my ears and the bass not as clear/punchy as I prefer. I run the bass at +3. I am considering purchasing a subwoofer, along with a DAC/DDC.
The room is roughly 450 sq ft with 10’-12’ coved ceiling. Looking for upgrade path suggestions for the mentioned 5k investment. Thanks in advance.