What are the limits of room correction/ treatments ?

Appropriate room treatment can make all the difference!  suggestions:
1.  Treat all wall intersections.  I have had Michael Green's Roomtune devices in mine for many  years.  
2. If the bass seems a bit much, bass traps may help.
3.  I like absorption behind the listening area so you aren't subjected to sound bouncing off the wall behind you.
4. Diffusors behind the speakers can yield substantial benefits.

If you Google, you can find a variety of products that may get you where you need to be.

Good luck!

It is amazing how the slightest adjustment to speaker location can yield significant results.  Not just placement...also the tilt back of the speaker for proper driver balance at your listening location and the degree of toe-in, if any.  It IS rewarding when you hit the sweet spot in your room.