Your choices are pretty simple. Room treatment and EQ. I use a combination of the two. I use the EQ built into Roon for the EQ and GIK acoustics panels and traps for the room treatment.
You might also want to look at the room mode calculator, it will help you see where you may have issues and what room locations to avoid.
https://amcoustics.com/tools/amroc
Based on the first 4 or so room modes, I'd encourage you to start with floor to ceiling soffit traps from GIK. First the wall behind the speakers, then behind the listener.