If I had a better idea of your room I could help with the bass issue. The 800hz issue sounds like a mechanical resonance, not an acoustical one. If I had to guess the tweeter is under damped suffering distortion. Is this your EPOS setup?

The panels you put up will lower decay time and reduce parallel flutter issues. They cant fix a bass null issue or mechanical resonance. frown You have to move the speaker or listener for Bass problems.