I don't think that a sub will help the problem you describe. I am a Harbeth fan at this price point for the quality and balance of the timbers. Owned monitor 30.2 with Ton Trager stands. It was an outstanding combo. The 30.2 is known for its mid-range and voices and the HL5+ are not as good in that range but have better bass and are more forward.it depends on musical presentation taste. You have to look at replacing the Rotel 1592 down the road however IMHO. Good luck and keep us posted.
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.