based on your measurements there is very little really wrong here,
the more pertinent question is what are you trying to accomplish?
just because you don't have a perfectly ruler flat curve doesn't mean your system isn't perfect as it is.
for most people a perfectly flat response is not desirable a bit of coloration can be a good thing as it creates a " more Musical sounding experience.
So the real question is what are you unhappy with? and why do you think a flatter response curve is necessarily better?
As as per acoustical treatment vs dsp acoustic treatments are always best as a dsp is always going to be in the signal path.
In our reference sound room and theater we strive for acoustical tuning first and then dsp as a final tune
Hope this helps
Dave and Troy
audio Intellect NJ