Have you tried experimenting with digital signal processing? If not, you might want to start with what is available in Roon (including equalization and upsampling). To take it up another level, with a correspondingly higher learning curve, take out a free trial of HQ Player. HQP integrates nicely with Roon, once you've figured out how to work the settings.
You also might want to try measuring your room frequency response with REW. Identify the bright spots, then focus DSP (or room treatments) there.